OKLCH is a polar coordinate space. Hue is angle in this space. So to interpolate hue from one angle to another, to get from one side of a circle to the other, you go round the edge. This leads to extreme examples like the one shown:
linear-gradient(in oklch, #f0f, #0f0)
You can also go round the circle the other way, which will take you via blue–aqua instead of via red–yellow:
linear-gradient(in oklch longer hue, #f0f, #0f0)
The gradient shown (in either case) is a good example of a way that perceptual colour spaces are really bad to work in: practically the entire way round the edge of the circle, it’s outside sRGB, in fact way outside of the colours humans can perceive. Perceptual colour spaces are really bad at handling the edges of gamuts, where slightly perturbing the values take you out of gamut.
Accordingly, there are algorithms defined (yes, plural: not every application has agreed on the technique to use) to drag the colour back in-gamut, but it sacrifices the perceptual uniformity. The red in that gradient is way darker than the rest of it.
When you’re looking for better gradients, if you’re caring about perceptual uniformity (which frequently you shouldn’t, perceptual colour spaces are being massively overapplied), you should probably default to interpolating in Oklab instead, which takes a straight line from one side of the circle to the other—yes, through grey, if necessary.
linear-gradient(in oklab, #f0f, #0f0)
And in this case, that gets you about as decent a magenta-to-lime gradient as you can hope for, not going via red and yellow, and not exhibiting the inappropriate darkening of sRGB interpolation (… though if I were hand-tuning such a gradient, I’d actually go a bit darker than Oklab does).
During its beta period, Tailwind v4 tried shifting from sRGB to Oklch for gradient interpolation; by release, they’d decided Oklab was a safer default.
Also, isn't the way browsers interpolate colors in sRGB just a bug that I assume is retained for backwards compatibility? sRGB is a logarithmic encoding, you were never supposed to interpolate between colors directly in that encoding - the spec says you're suppose to convert to linear RGB first and do the interpolation there...
It's not a bug, its a property of the colour space. Which is partially tied to how the colour is represented (RGB). When doing linear interpolation through the RGB cube (for eg a gradient), you normally pick the shortest path. It just so happens that sometimes that path passes thorough some shade of gray as different colour components are scaled.
Usually you fix it by moving your point through a different colour space. Choice depends on your requirements and mediums you're working with (normally different types of light sources or screens).
I had to write a low level colour interpolation librar for a few interactive art projects, so I dipped a bit into this, but I'm no colour expert
No, sRGB refers to both a colour space and an encoding of that colour space. The encoding is non-linear to make best use of the 256 levels available per channel, but you were never supposed to interpolate sRGB by linearly interpolating the encoded components: you're supposed to apply the transfer function, perform the linear interpolation at higher precision, and then convert back down into the non-linear encoding.
Failure to do this conversion is what leads to the bad results when interpolating: going from red to green will still go through grey but it should go through a much lighter grey compared to what happens if you get the interpolation wrong.
I think GP is referring to the difference between "normal" (gamma-encoded) sRGB and linear sRGB. Though it's not logarithmic but a power law. In any case linear interpolation done in non-linear sRGB gives you intermediate colors that are darker than they should (though historically it's been so common in computer graphics that people are accustomed to it).
>During its beta period, Tailwind v4 tried shifting from sRGB to Oklch for gradient interpolation; by release, they’d decided Oklab was a safer default.
I recently implemented both, first I started with OKLab which turned out really well, the gradients you get from it are amazing and the usual color sets (analogous etc.) produce really pleasing sets.
However I quickly ran into the main problem with it, which is that fiddling with its Lightness, Chroma and Hue dials doesn't produce human understandable results. For example sometimes changing L or C induces a color shift, or for some given values changing L only gives midrange values that doesn't go up or down all the way.
I then implemented OKLCH on top of that, which was the way I assumed everyone was doing it. Just have it act as the controller for the human layer, then convert to OKLab for creating gradients etc. The article doesn't really go into it, but having OKLCH as the frontend controller fixes the LCH sliders such that they produce values that make sense to us humans, while still having the superior OKLab setup in the back.
IMO in pretty much all cases if the two colors at the end of your gradient are not already very close, you will always get the best results by manually specifying the colors at one or more steps between the two original colors.
Which brings me to point at the crux of the matter: avoid gradients between two dissimilar colors in the first place.
For others, I'm sure parent knows: OKLCH is largely a bugfix for CILEAB. Both try to make a color space where even steps feel evenly spaced to a human. But CIELAB had procedural flaws in its creation.
See slide 19: https://www.w3.org/Graphics/Color/Workshop/slides/talk/lille... -- if you ask CIELAB to make "pure blue" (RGB 0 0 100%) become grayscale, the intermediate colors become purple to the human eye. The entire point of a perceptual color space is that that doesn't happen. OKLCH fixes that.
BTW, credit to Björn Ottosson, who basically side-projected a color space into the web standards and more: https://bottosson.github.io/posts/oklab/ ... folks like him are why we sometimes have nice things!
A good gradient is one that takes a perceptually uniform, and typically perceptually shortest, path. The OKLCH gradient isn't perceptual uniform and appears to take unnecessary detours through other hues.
Gray is arguably just another color, it’s not clear why you’d want to avoid it. How is going via red and yellow better than going via gray? Varying hue is often perceived as a larger change than varying saturation or lightness. A path going through several distinct hues is visually less uniform than one going through gray once.
Is gray perceived as "just another color" or where all colors go when desaturated? I assumed the latter, which would explain why to avoid it if one isn't playing with saturation.
Think of fashion, of smartphone colors, pen and pencil colors and the like. Gray, white, black, are just color choices among all the available colors. A gray T-shirt isn’t a desaturated colored T-shirt. It’s its own color.
Color is weird like. Gray is “all the visible spectrum in equal proportions”, which is white… just less white than the whitest thing visible but more white than the darkest (blackest) thing visible.
It’s a “color” because it’s useful to describe such a thing. If you had monitor entirely filled with 50% white you’d call it white. Only by comparing it to something brighter do you call it gray. Brown is the same thing. In a dark room if you looked at a monitor filled with red and green pixels you’d call it orange. Only when you start adding in clues like whites and brighter colors would you call it brown.
Anyway, yes grey is a color. But it is not quite the same as other colors. Other colors occupy only parts of the visible electromagnetic spectrum. Whites are the whole thing.
There is actually several very good technology connections videos about this stuff. Color is very cool!
...with varying definitions of "whole". D65 white is almost blue when compared to A white. It stops being either “all the visible spectrum" or "in equal proportions” pretty quickly once you look closer at it.
Oh, I understand what you say. But in color spaces, isn't gray the "sink" towards which desaturated colors shift? This would make it a location to avoid (unless you're purposefully desaturating).
> Aren't these in direct conflict? If you can't resaturate it, that implies it's not desaturated.
Kinda. There's a singularity in the math. The problem is that hue is defined as an angle and saturation is defined as distance from the center, but there's no consistent way to define a direction for the origin. Black and white have the same problem because they're also desaturated.
> And if you buy a forest motif, people will be upset if it's pink. That's just doing a tie-dye wrong, not a rebuke of whether it's a color at all.
I'm not arguing that it's not a color, just that it doesn't belong in all gradients!
Of course it doesn't belong in all gradients. It would only be in gradients that go from near-opposite colors. Or if you mean pure gray it would only be in gradients between exact opposite colors, and there are no good options for such a gradient.
I mention tie-dye because it feels like a quintessential example of a color gradient. I think it's perfectly reasonable to ask for a blue and orange tie-dye shirt and perfectly reasonable to not want grey colors simply because they're on opposite sides. I could see white in between, I could even see black, or I could see purple and red or cyan and yellow. I don't think there's a universally right answer here!
Someone asking for those colors doesn't actually want a gradient with two anchor points. So yes there are many answers but because it's not a quintessential example of a gradient.
> I thought the same until I googled "blue and orange tie-dye." I'll be honest, more white and black than I expected!
Putting white or black in between adds another anchor point.
And looking more around examples of blue and orange tie dye, most aren't really gradients overall, they have big splotches of solid color with small gaps or overlaps in between, and at least half the time the gaps and overlaps don't even have a gradient inside them.
> We may have to agree to disagree that tie-dye isn't a quintessential example of a gradient. Would you argue that rainbows aren't either?
Hmm. How about this. I would say a rainbow is not a gradient between two colors, and the color space discussion is about a gradient between two colors. The exact border of "quintessential" is not something I really want to spend too much time on.
In my mind a gradient is simply a smooth transition between colors with no universally agreed upon definition. The choice of specific curve through colorspace is rather arbitrary. It seems perfectly reasonable to want to include grey and perfectly reasonable to want to avoid it.
Let's say you continuously change wavelength of a laser from blue (~480nm) to red (~630nm), you are going through green, not through gray. If in your use case going through gray makes sense, that's ok, there may be many paths from one color to another.
In general people don't really think of color in terms of the spectral progression (or the hue wheel), and I don't think that most people intuitively expect a gradient between two colors to pass through another "unrelated" primary or secondary color. The point is somewhat moot though, given that such gradients (like yellow to blue or red to green) are very unnatural anyway.
I disagree somewhat. Color mixing just isn't particularly intuitive. It's not the most intuitive to get a third hue, but that doesn't justify grey (which has an undefined hue). I do think most people are quite comfortable with the fact that between blue and yellow exists green, but is it a saturated green or a desaturated green? Additive and subtractive color mixing behave very differently here.
It's funny and a bit sad because we just went througha decades-long effort to migrate away from jet/rainbow gradients to vik/batlow/bi-hue gradients, and now rainbow is forcing its way back.
Honestly I suspect this is largely a non issue. I have never made a gradient that goes through more than 2 different color (by some vague measure of different) without adding an additional stop. If I wanted to go through yellow and green to get to blue, I would add a stop at yellow and another at green, and I suspect most developers would do the same.
Is that not a transition through the color mixing (or overlay). I'm assuming the light sort of tails off as you leave the area of one color and head to the other (and the other color comes on with more intensity then).
I suppose that's different with light than some analog with pigments? (Two dabs of color set apart, a brush perhaps used to blend them as continuously as is possible.)
Your light thought experiment would produce a color gradient via additive color mixing.
A magenta to green gradient would then go through white rather than grey. A subtractive magenta-green gradient would go through black. Not sure what physical setup would produce the latter gradient. But the standard RGB (or OKLAB) gradient goes through grey rather than white or black. This type of gradient is physically created by dithering: Dithering a gradient from magenta to green, by just using these two base colors, would produce a perceptual grey in the middle. This type of color mixing is otherwise better known as alpha blending.
It depends on how you think about your spread. If, as someone else said, you're trying to represent a tunable laser going from red to blue, going through gray is completely wrong. That is not what a laser will do, ever. It will always be a fully saturated color.
So, depending on what you're doing, you want different things. You may want to view your color space as an RGB cube, and go through gray. Or you may want to view your color space as something more like HLS or OKLCH, and not go through gray.
Gray is arguably not just another color; I don't know about English but in German you have 'bunte' and 'unbunte' colors; 'unbunte' colors are white, black, and the grays in between
It's an ugly color. Saturation makes stuff pop; this is often desirable. This is why I think it's important to have both polar (OKLCH) and rectilinear (Oklab) gradients.
Interesting. In nature, I suppose I am most aware of a gradient from a saturated azure sky above to a much whiter sky on the horizon. This would seem to be a trivial saturation gradient.
For a spot color (from a gel covering a light) the light diffuses further from the center of the projected light — two spot colors (with different gels) then, next to each other, would give a kind of gradient from one color to the next as you walk a line from the center of one light to the other.
I wonder what the closest analog to this is algorithmically?
I guess where I am going with this is: is there precedent in nature as to how gradients are supposed to work (and therefore an analog which we should try to model) or are we going strictly on how the human eye perceives color and what algorithm we think "looks" right?
> you should probably default to interpolating in Oklab instead
The article says as much. Quoting:
> This can be a double edged sword. While some gradients might look smoother, you might also see colors that you've never defined. This is because hue in OKLCH is circular and gradients can take unexpected detours.
> To avoid this, many tools use OKLAB for gradients, which interpolates in a straight line and gives more consistent results.
Making a gradient from two colours on opposite sides of the spectrum is a bit of a pathological case. There's no obvious answer what it "should" look like, and also no good reason you'd really need to do this. If you're using a gradient as a design element, you'd pick your own midpoints.
Very interesting. Is this just a limitation of our current hardware? How much of this problem would still exist if everyone had a wider gamut monitor, say full DCI-P3? That still doesn't cover the full gamut of Oklch, but would it make the problem practically disappear?
No. We’re talking about colours way beyond the ranges of human perception.
For this specific gradient, see https://oklch.com/#0.7017,0.3225,328.36,100 and https://oklch.com/#0.86644,0.294827,142.4953,100, and look at the Chroma panel, see how far out of our screen gamuts they are (even tick “Show Rec2020”, which adds a lot of chroma around blue–green and magenta–red), and try to imagine the colours between the lime and magenta (in either direction). The red direction is probably the easier to reason about: there’s just no such colour as a light, bright red. You can have bright or light, but not both. (Its 3D view can also be useful to visualise these things: you’re building a straight-line bridge between two peaks, and there’s a chasm in between.)
I don't get it, why am I seeing the "out of gamut" colors if my sRGB monitor is unable to display them? Would the charts look different on a P3 monitor?
edit: Also, you mentioned the colors "beyond the ranges of human perception" but I don't think there is any such limitation here, the bottleneck is the hardware (computer monitors).
I don't understand why HN sometimes responds aggressively to an honest, puzzled question. It's as if being wrong (or confused) was a sin here, sometimes.
I thought yours was an honest question that warrants an answer (which thankfully Chris answered).
But once an algorithm to drag the colours back in-gamut was applied, would the lost perceptual uniformity still be a problem practically speaking, with DCI-P3 monitors?
Yes. I repeat: these colours are way outside gamut. Not just a little bit. P3 helps a little bit, Rec.2020 would help a fair bit more, but you’re still asking for a yellow that is about twice as vibrant as is possible.
The underlying problem is that the color space humans can see doesn’t have nice uniform linear boundaries. The larger your color space, the more relevant that issue actually becomes.
That gradient looks terrible, very bad colour banding, because you’re starting and ending at points that are way out of gamut, and the technique used to bring it in isn’t smooth. For a gradient like that, you probably want at least five points.
That is the biggest problem with these colour spaces: the edges are unclear, and overflowing them has bad effects.
- how to easily add "warmth". you can't just add red+green
- no good tools for it (e.g. a nice gradient picker ui that lets me specify if I want to allow running out of bounds of teh color space and clip a few colors at max saturation)
Also check out oklch.com, I found it useful for building an intuition. Some stumbling blocks are that hues aren’t the same as HSL hues, and max chroma is different depending on hue and lightness. This isn’t a bug, but a reflection of human eyes and computer screens; the alternative, as in HSL, is a consistent max but inconsistent meaning.
Another very cool thing about CSS’s OKLCH is it’s a formula, so you can write things like oklch(from var(--accent) calc(l + .1) c h). Do note, though, that you’ll need either some color theory or fiddling to figure out your formulas, my programmer’s intuition told me lies like “a shadow is just a lightness change, not a hue change”.
Also, OKLCH gradients aren’t objectively best, they’re consistently colorful. When used with similar hues, not like the article’s example, they can look very nice, but it’s not realistic; if your goal is how light mixes, then you actually want XYZ. More: https://developer.mozilla.org/en-US/docs/Web/CSS/color_value....
Also, fun fact: the “ok” is actually just the word “ok”. The implication being that LCH was not OK, it had some bugs.
Aside from a few criticisms that others have already raised I think this is quite a nice introduction to OKLCH and how to use them in CSS.
With that out of the way, I'd like to go on a tangent here: can anyone explain the modern trend of not including publishing dates in blog articles? It stood out to me here in particular because the opening sentence said that "OKLCH is a newer color model" and the "newer" part of that sentence will get dated quicker than you think. The main site does mention a date, but limits it to "August 2025" so this seems like a conscious choice and I just don't get it.
> can anyone explain the modern trend of not including publishing dates in blog articles?
In such cases, I usually try to see if the `Last-Modified` header served with the HTML document over HTTP, can be useful, but I conclude that often the same people who don't bother with dating their content -- you'd think they'd understand where the word _blog_ comes from, as in "[web]-log" where timestamps are paramount -- these same people don't know or care how HTTP works. Hint: the `Last-Modified` is the last modification time of the _resource_, in this case the actual HTML document. Just because your "backend" re-rendered the content because you didn't bother with setting up your server caching correctly, doesn't mean you should pretend it's a brand new content every day (which https://jakub.kr/components/oklch-colors does, unfortunately, so you won't know the timestamp from HTTP).
I would imagine this is rather to whatever "blog engine" is used instead of the conscious choice of the author (even if they knew what they desire and what would qork better, it might not be their priority).
I can't explain it, but undated articles are a serious problem. I don't know whether it's a modern trend ... how can one tell in the absence of dates? I've seen plenty of undated content that appears to be old.
On some blogs I can only tell the timeframe of the content from the timestamps on the comments ... but many blogs like the OP's don't support comments. I'm not likely to revisit them. (The blurb on the OP's main page is ironic ... rather than obsessing over the smallest details I see obsession over esthetics to the detriment of functionality.)
> In the example above, you can see that the OKLCH colors maintain consistent blueness across all of the shades, while in the HSL example, the lighter shades drift to purple and the darker ones muddy out towards grayish.
There is a very clear shift towards green in the OKLCH lightness value change example, enormously more so than any purple vibe in the HSL example.
Clearly being able to select colours of the same perceptual intensity has value, but some of the claims here as to the benefits are exaggerated.
To increase brightness past the limit of the Hue band for the color, the rendered output color on a display shifts cyan due to the limited brightness range of a saturated blue in the Display P3 color space. OKLCH is, when varying brightness along a gradient, Saturation-invariant rather than Hue-invariant; whether that effect is desirable is a matter of aesthetic preference, but after decades of Hue-invariant desaturated web color, it’s certainly refreshing to have a choice about which compromised invariance to take.
Science recently invented a much-deeper blue LED than we have now, so I expect in a decade or two, whatever ends up succeeding Display P3 will be much more able to represent that gradient without cyan-shift, and all of the years of OKLCH gradients created before that time will end up showing a more accurate blue gradient with only the colorspace change. In the meantime? Do whatever’s aesthetically pleasing; there is no Right Answer in design :)
ps. One could argue that a post-OKLCH colorspace should not accept the binary decision of Hue or Saturation invariance, and instead should be Saturation-invariant to the display’s native limit and then transition smoothly to Hue-invariance at that threshold. I believe that’s a Difficult Problem in color profile specification terms, since it isn’t just pre-calculating the changeover threshold for all monitors (not to mention, do you change blue sooner or same as red, etc) but it’ll be a while longer before I’m versed enough in ICCv4 to explain that perception. It sure would make for an interesting experimental DisplayCAL target, though!
The hue isn’t shifting in OKLCH at all; also, it’s definitely shifting when OKLCH is rendered to Display P3 or sRGB. This is normal and expected behavior for colorspace gradients when rendered to device profiles? But I suspect I’m too close to the problem to see what’s not explained properly, apologies.
Your viewpoint of there being one true way of spectrum gradation under restricted device domains is not universally agreed upon; neither among designers, nor among the ‘normal’ population. No other way is the one true way, either! What works well for a PC sRGB display will be drab and lifeless on a laser cinema projection systems. Printers have faced this problem for centuries and innovated to use glass (long ago) and brushed-metal prints (more recently) as a way to regain control of luminosity independent of saturation and to express their design in less restrictive ways. The only ‘normal’ in this scenario is the shared agreements we make, and the primacy of sRGB’s desaturated brights as the sole exclusive agreement is ending.
(Since this reminded me of it, a random pro tip: For those using macOS Terminal.app, you can redefine the 16 ANSI colors using the full P3 colorspace, so long as you use the full GUI color picker rather than the sRGB-limited #rrggbb entry method. Access to improved saturation helps the eye distinguish different shades in the dim and bright color sets more effectively without having to alter their brightness. It won’t improve the limitations of ANSI color as a whole — the insistence on Luminosity = f(R,G,B) is baked into everyone’s assumptions quite deeply thanks to sRGB! — but it does at least mean you can have seven equidistant and non-desaturated, non-sRGB colors at two levels of brightness for syntax highlighting and other typical 16-color uses.)
I opened the macOS Digital Color Meter and set it to "native values" mode. The second-to-last OKLCH swatch has a green component of 202, and the last has a green component of 226. The corresponding values in the HSL swatches are 203 and 227.
It's visibly cyan, isn't it? It's maybe not an intuitive "green" hue (depending on your linguistic culture), but it's clearly different from all the other colors on that chart.
Agreed. The hue changes completely from blue to cyan.
If that's a correct implementation of OKLCH, then it's not something I would ever touch. Something seems to be deeply wrong with however they're calculating hue.
HSL/HSV have issues with perceptual lightness. But not with hues. The hue is constant and doesn't need any correction depending on saturation or lightness.
I think you do usually want to rotate the hue a bit when changing the lightness though. It’s a difficult thing to get right and one of the reasons the tailwind builtin colour palettes are so useful.
You don't. That's not something graphic designers ever do as compensation for perceptual uniformity.
I looked into it a bit more, and it turns out it's a result of OKLCH easily producing colors out of gamut, and then choosing to sacrifice hue accuracy for better saturation accuracy.
That's a fundamental design flaw if you ask me. Changing hue is completely unacceptable in my book.
In "Refactoring UI" [1] (by the creators of tailwind) they recommend when designing your shades for a single base colour:
> Since different hues have a different perceived brightness, another way you can change the brightness of a color is by rotating its hue.
> To make a color lighter, rotate the hue towards the nearest bright hue — 60°, 180°, or 300°.
> To make a color darker, rotate the hue towards the nearest dark hue — 0°, 120°, or 240°.
> This can be really useful when trying to create a palette for a light color like yellow. By gradually rotating the hue towards more of an orange as you decrease the lightness, the darker shades will feel warm and rich instead of dull and brown
You could argue whether this is "perceptual uniformity" or something else, but the fact is that to create a realistically useful colour palette with a bunch of shades, you definitely cannot simply use HSL, keep the hue constant, adjust S/L. It's not that easy (and OKLCH doesn't make it that easy either).
sRGB is already not perceptually uniform. These hue changes already happen. Just because the H value in HSL/HSV doesn't change doesn't mean there's no perceptual hue shift when adjusting lightness/value.
I don't know what you're talking about -- that isn't true.
There is absolutely no perceptual hue shift in the HSL/HSV models depending on saturation and lightness/value, or when they get translated into sRGB. That's the entire point of HSL/HSV, to isolate hue and hold it constant.
HSL/HSV are not perceptually uniform in terms of brightness when hue is changed, or even brightness linearly. But hue is hue. Perceived hue does not change based on brightness or saturation.
There most definitely is perceptual hue shift in HSL (and HSV); it's illustrated quite well at [0](The blog of the creator of OKLab), particularly in [1], an image showing S and L axes while leaving H fixed.
Well I'll be damned, you're right -- I'm playing with it in Photoshop now, and it seems to be exclusive to hue values of 233-270, in the transition from blue to purple, and nowhere else. Matches what [0] says -- "This is particularly obvious for deep blue and purple colors."
So first, thank you for the correction. It's fantastic to learn something new. And second, do you have any idea why the OKLCH example on the page is so atrociously bad? The way blue changes to cyan is even worse than the HSL/HSV difference of blue-purple. It's like the cure is worse than the disease. If they were so concerned with hue fidelity in the first place, I'm surprised they wound up producing an end result just as bad.
I don't know much about the science of colors and I imagine this is going to be very subjective but I would at "worst" describe the rightmost OKLCH color as blue-green (but probably just "light blue"). Meanwhile the two rightmost HSL colors I would not describe as blue at all. Second from right I would call "light purple" and the rightmost honestly looks grey to me (which is weird because the caption says the darker HSL values "muddy out towards greyish" but the leftmost values for OKLCH and HSL both look pretty blue to me).
Also if I use the macOS app "Digital Color Meter" I get essentially the same green value for the rightmost OKLCH and HSL colors (226 and 227 for "display native values" and 228 and 227 for sRGB).
While the above site is great for measuring with a modern contrast algorithm (it’s the current algorithm for the yet-to-be-released WCAG 3 accessibility standards), it’s worth bearing in mind that the WCAG 2 algorithm is somewhat different, and a legal requirement in many markets / industries. You can check your colours against that with a tool like https://www.siegemedia.com/contrast-ratio, although there are many more.
You can pick colors that pass both APCA and WCAG contrast checks though so it's not a problem to use APCA recommendations now.
I find APCA is a little stricter than WCAG for light themes, and APCA is much stricter than WCAG for dark themes, to the point where you really shouldn't use WCAG for dark themes. So most of the time APCA is giving you stricter contrast that easily pass WCAG also.
I keep seeing mentions that APCA will let you finally use e.g. white on orange, or white on vibrant blue that pass APCA but fail on WCAG, but my feeling is there's not a lot of examples like this and most of these pairings only have okay contrast anyway, not great contrast, so it's not ideal to be stuck with WCAG's false negatives but not that big of a deal.
If your colours have enough contrast to pass them both then of course that’s fine!
I only bring it up because I had a situation last week where the better APCA was giving results for both white-on-colour and #111-on-colour as suitable for headline copy under WCAG3, but #111-on-colour was 7.5:1 and white-on-colour was 2.5:1 under WCAG2, hence we could only use one of them legally.
> I only bring it up because I had a situation last week where the better APCA was giving results for both white-on-colour and #111-on-colour as suitable for headline copy under WCAG3, but #111-on-colour was 7.5:1 and white-on-colour was 2.5:1 under WCAG2, hence we could only use one of them legally.
Yeah I understand, would you agree this is fairly rare when using APCA though?
I've had the opposite where the brand guide was suggesting we use a light on dark combo that passed WCAG2, yet it failed APCA, and worst of all clearly had poor contrast just by looking at it. Yet, some people will still go with it because WCAG2 gave it the okay haha.
Maybe you've seen this but there's also https://github.com/Myndex/bridge-pca that does the "this color pair passes both APCA and WCAG2?" check in one pass.
As per discussion of this new OKLCH idea in TFA - Are we even sure we have great formulas for measuring/defining contrast in the first place? Do you agree / disagree with any of the counterexamples over at: https://github.com/tattoy-org/contrast-experiments
I'm not following. These examples are using the WCAG2 contrast algorithm which is well known to be flawed for people interested in this stuff, especially for dark themes so there should be lots of bad examples here? APCA is supposed to improve on this (see the example graphic comparing WCAG2 and APCA): https://git.apcacontrast.com/documentation/WhyAPCA.html
> But as @c-blake has rightly pointed out, this doesn't take into account the ratio of visible background pixels to foreground pixels. For example the contrast required for a single fullstop character, ".", is goting to be diffrent from a capital, "B".
So APCA includes more guidance on font weight and font size for more contexts (e.g. headings, body text, shorter text, copyright notices), but it's still going to be an approximation for edge cases like displaying a single fullstop character. If this case is common, you'd want to increase the contrast value instead of going with the minimum passing value, so the contrast algorithms can still help you.
There's a tradeoff with having guidelines that are very accurate (e.g. a contrast algorithm that counts pixels) vs simpler to follow (e.g. recommended font weight and size). People already find WCAG2 hard to follow as it is.
I don't think you & I have much disagreement here as I like the way you write about approximations and edge cases and things involving human judgement calls and "both not either" kinds of testing. The WhyAPCA document you link to also includes language to such effect with sliding scales over regions & such. Me - I'm mostly asking questions not offering answers. That said, to correct the record..
>These examples are using the WCAG2 contrast algorithm which is well known
Only one of the 4 tables shown is the thing you say is the known-to-be-flawed WCAG2 one. Some counterxamples are listed for all 4 formulas, though, 2 of which use the CIE Lightness (which, sure, is probably different, but I believe the CIE L is what APCA is based upon - in spite of so..many..words on their doc pages they often just say "lightness").
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Another point of those 4 tables, perhaps more clear when looking at the python script, is whether "numerical ratio" vs abs(difference) is better. It seems to me that color space designers, like this OKLCH, are going after "perceptual linearity" which suggests abs(diff) is far more appropriate than a "ratio" which has "near zero" troubles (and zero & one are downright seductive numbers for perceptual lightness scales).
I certainly should learn more about it, but various "click through" APCA things I've seen seem to speak in ratio terms like "10 times the contrast" (though admittedly that only assumes some scale for contrast not that it's formulated as a ratio - it's just suggestive). So, I should probably look more into it before actually offering a critique, but it still has the feeling of "cross purposes" - using some color space axis designed for [0,1] linearity differences instead for ratios within that axis. When I tried using the WCAG2 one I was kind of stunned how sensitive everything was to what should have been a kind of "arbitrary adjustment" to handle near-zero.
I might wonder what designers of color spaces actually have to say about this ratio vs. difference issue if you know of any articles. You seem knowledgeable. The spaces seem literally designed for differences to me.
Your link itself admits the 0.05 makes it a different formula. Both Y and L* go to zero for hard black which is a very common color (the most common for me) and would be infinite with black in there. I disagree this is all "not real".
The 2x2 table in that contrast experiments link I sent enumerates some differences along the edge cases { even with just |diff|s. }. Just empirically if you change that 0.05 to 0.02 or 0.10 things change "a lot" in terms of all the edge cases. You can try fiddling with running that Python script yourself and see.
Also, I believe the project of an actual "contrast measurement" - not merely threshold checking - is a worthy goal. I think it would be good to be able to say how bad, and for that the specific monotonic transformation absolutely matters, and again, I expect the color space designer people have opinions on this very worth listening to. I think they are targeting differences in the numbers being the most meaningful thing.
All that said, I did like your George Box quote. :-) I just don't think dismissing the problem is a great solution here. I'm not sure there is a great solution. But you & anyone are always free to find any problem uninteresting. I mean, you could also find all the color space distinctions of TFA similarly "no real difference".
On the comparison between Color spaces, it's weird, my monitor from 2008 does show a difference between the Display-P3 and the sRGB purple colors, yet I didn't think it'd have such a big color range. Is there some color conversion at the browser or OS-level? (my distro/desktop enables colormgr by default).
The first uses oklch(0.65 0.20 300), comfortably inside sRGB, not even at the boundary. The second uses oklch(0.65 0.28 300), which is well outside P3 and even Rec.2020.
The smallest fix would be to make the second one oklch(0.65 0.2399 300) to bring it inside P3 so the demo doesn’t get slightly warped if Rec.2020-capable (not really necessary, but preferable, I’d say), and the first #a95eff (oklch(0.6447 0.2297 301.67)) which is CSS’s fallback.
But purple is also pretty much the worst choice for such a demo—P3 adds the least to sRGB around there, so the difference will be smallest. A better choice is red or green.
So a better pair would be oklch(0.65 0.2977284 28) on the right (a bright red at the very edge of the P3 gamut, well outside sRGB) and #f00 on the left (the sRGB value CSS will map it to if out of gamut).
Sort of off topic questions, do we have any upcoming colour space beyond BT2020, now that we soon have monitor that reach 100% BT2020. I did some search and it doesn't seems to be any.
For any really bigger color space, you would have to use more than 3 primary colors, which would increase a lot the cost.
Moving the monochromatic BT.2020 colors from 630 nm, 532 nm and 467 nm could get a little increase in color space coverage, but at the expense of a lower efficiency in power consumption to brightness conversion. 467 nm is not a very pure blue, but the sensitivity of the eye drops very quickly in the blue region, so a better blue would require much more power. Similarly, though not so pronounced, for a different green.
Moreover, in the green region there is a gap, both for lasers and for LEDs, where the available devices have low efficiencies for converting electrical power to light, so changing the frequency of the primary green color would have to take that into account too.
In conclusion, I believe that the BT.2020 (actually BT.2100) color space is close to the best that can be done in displays of reasonable price and energy efficiency.
A true coverage of 100% of the BT.2100 color space can be realized only with laser projectors. Any display with LEDs or quantum dots will never have really monochromatic primary colors, though a coverage of significantly more than 90% of the BT.2100 color space is not too difficult. However, the advertised percentage of the color space may be misleading, because it varies depending on the kind of color space used for computations. A coverage percentage computed in OKlab would be more informative than a percentage computed in the XYZ color space.
> For any really bigger color space, you would have to use more than 3 primary colors, which would increase a lot the cost.
Unless you want to make displays for the bees and birds (and the tiny alleged minority of human tetrachromats) that seems rather pointless. People with three color receptors are your customers, so that's driving the market.
I rather predict, future displays will further improve on contrast, including very bright (brilliant) sparks. Imagine an iPhone glittering like gold or diamonds ...
The border of the color space corresponding to monochromatic colors is convex, so any triangle inscribed in that curve border will leave parts of the color space that cannot be reproduced on a display.
The convexity of the border means that if you compute the 3 coefficients of RGB colors that match a desired color, there will always be some colors that need one negative coefficient, regardless of the choice for the RGB primary colors. On any display, it is impossible to realize a negative brightness of a color, so on a RGB display there will always be some colors whose hue and brightness can be reproduced, but their saturation cannot be reproduced.
The only way to make smaller the parts of the color space that cannot be reproduced is to take more points on the monochromatic border, replacing the triangle of reproducible colors with a polygon that fits more closely the curved border.
The entire color space perceived by humans could be reproduced on a display only with tunable lasers, not with fixed-frequency primary colors. One could use fixed-frequency primary colors only if they would stimulate directly the photoreceptors in the eye, to enable workarounds for the overlapping filter characteristics of the cones and for the signal processing done in the retina.
That's not the issue. Take pure blue wavelengths as an example. They also activate your green cones a little. Increasing the frequency activates the blue cones less and the green cones much less, yielding a higher ratio of blue to green activation, and a new color (violet) that you can't represent with mixed color output exactly aligning with mode receptor wavelengths.
> This way the browser uses OKLCH colors if they are supported, otherwise it falls back to sRGB.
This wording suggests it’s about gamuts, but it’s actually about syntax. It will use the oklch() if that syntax is supported, and then the OKLCH value may be within sRGB or may be in another gamut the screen is using or may need to be mapped back to the screen’s gamut. Whereas #rgb values are inherently limited to sRGB, the baseline.
I tried working with it but had to give it up for practical purposes. Whereas the focus with HSL is on the Lightness part and the Saturation is made to fit, OKHCL does it differently. It pushes the Chroma part to it's technical limits and abuses the Hue to make it fit, but we just do not understand Chroma intuitively.
I am waiting for OKHSL where the adjustments will bu much smaller and do not lead to absurd changes in intent.
I already had a discussion about it somewhere else (https://www.reddit.com/r/css/comments/1jv5f0r/hue_is_an_issu...)
Why is there no documented formula to convert to from this color space? A quick google and the best I could find is this Gist[0]. Searching for Oklab has a Wikipedia page[1].
It looks to me that all the "magic" is in the matrices used for conversion between Oklab and sRGB. The final conversion between Oklab and Oklch is trivial, and is documented in your linked Wikipedia article.
Nice post. OKLCH is quite handy but for writing colors in CSS I hope eventually we’ll get some form of OKHSL/OKHSV[1] so users don’t need to worry about gamut boundaries.
There is a youtuber (Gneiss Name) making educational content through the medium of Minecraft.
He's made one on OKLab as well: https://youtu.be/nJlZT5AE9zY
That's quite misleading. The parent commenter was asking about gradient (interpolation between colors). Gradients look completely different in oklch and oklab.
Well yes, it's a different coorsinate system, so gradients would look different. It is still the same color space, but I agree I could have worded that better.
Does anyone know how this is different to the Munsell color space, which is also perceptually uniform?
Edit: I would imagine that the only way to definine a perceptually uniform color space is by tons of user testing. This is how Munsell developed his color space… specifically presenting test subjects with pairs of identical and near-identical color swatches and asking if they could tell the difference.
In this way, pairwise comparisom of similararity became the bedrock of color perception science.
The Munsell color system isn't really intended for displays, rather it's a collection of pigments, similar to Pantone. The transforms can get a bit weird (for example, since the swatches are discrete, there's no defined way to get intermediate colors). Munsell's ideas, particularly the axes of hue, value, and chroma, have absolutely influenced modern color spaces and are very much on display in the OKLCH space.
The best axis for Lightness in my opinion is still the Gray-Scale (as used back in the day for black/white/grayscale TVs).
The newer CIE colorspaces (CIECAM02 CIECAM16) seem to address the effect, that color-perception goes wild if you change background and illumination. Oklab seems to only make some fixed choice about how to include the chromatic part to lightness. I'm not so sure, how this definition of lightness is any better than grayscale (from 1931).
> The way gradients work in OKLCH is pretty different compared to sRGB. In sRGB, gradients are calculated in red, green, and blue values, which often leads to muddy midpoints and uneven brightness.
I always understood those “muddy midpoints” as a failure to properly gamma correct the interpolation between two (s)RGB colors. Is that happening here, or is the mud coming from something else?
Grays run along a diagonal axis of the RGB cube after stripping gamma off. A straight line through the cube will brush by it. This is enhanced when transitioning from a primary (green) to an opposite corner (magenta).
I added oklab to emacs's color module. I initially intended to use it to make better procedural themes, but I haven't gotten to that yet. In any case, emacs version 30 has color-oklab-to-xyz and color-xyz-to-oklab functions that work with the other functions in emacs's color module to convert to/from oklab colors.
"In the example above, you can see that the OKLCH colors maintain consistent blueness across all of the shades, while in the HSL example, the lighter shades drift to purple and the darker ones muddy out towards grayish."
The OKLCH lighter shade veers off into bright cyan! I don't see HSL getting grey on the dark side.
This is fantastic, can't wait to incorporate it into my web design classes stuff.
Also, I do hope people begin to see the value of "designing toward intuition," I can't help but notice that efforts like these are exact opposite of what happened when (most of) the world forcibly converted to metric.
> It also works the other way around, where you can change the lightness value to create various color shades and there is no hue or saturation drift unlike in other color modes.
> In the example above, you can see that the OKLCH colors maintain consistent blueness across all of the shades, while in the HSL example, the lighter shades drift to purple and the darker ones muddy out towards grayish.
I see lots of automatic palette generator projects where the shades of each color are generated with OKLCH by only varying the lightness value on some chosen base color. The problem I find is if you look at popular open source palettes, the way the hand-crafted hue and saturation values vary across the shades for different hues isn't that predictable (the curve of the hue/saturation values over shades aren't straight lines or typical easing curves).
Hawking my own tool (using HSLuv with RGB for now), but you can load and compare the hue and saturation curves as they vary over shades of a color using example palettes from Tailwind 3, USWDS and IBM Carbon, plus tweak each shade to your liking:
So I think OKLCH is a nice starting base for palettes and a quick way to generate a color you need in CSS, but I think designers will always need to tweak the hue and saturation of each shade so it looks just right as there's no single right answer you could encode into the color space.
Hi Alexei, thanks for your work on HSLuv! I love the simplicity of it, where you can use HSLuv as mostly a drop-in replacement for HSL which most designers are familiar with.
I keep seeing new tutorials on designing accessible palettes that still use HSL, where the WCAG2 contrast breaks and goes all over the place as you vary the hue and saturation. HSLuv makes life so much easier here and lets you focus on exploring colors that you know will pass, using a familiar looking color picker.
colors are much more accurate in terms of
how humans perceive them and it makes
working with them much easier
This is an aim, which I am not sure fully addressed.
Think of the reason why can't I get oklch or any other method of color definition in HTML to produce the "gold color" as we humans think of it.
The fundamental reason you can't get a truly convincing "gold" color using a single value in oklch, rgb, or any other color definition is because gold is a material, not a color.
What our brain perceives as "gold" is not a single, flat hue.
It's a complex interplay of light, reflection, and texture.
Point is, even with sophisticated CSS involved with linear gradient it is still a challenge
jesus fuck the whole discussion here is ptsd inducing... you need at least color accurate monitoring (including $25-30K calibrated monitor if you want to discuss rec2020-beyond) before judging if the output color looks "correct", and as correct here includes perceptually uniformity, then your monitor is crucial since light emitting technologies in the market are wildly varied.
this is _especially_ vital if you're not from color science & color correction industry, because that means you have no prior experience(s) with many problems & implications faced in the last 30 years of say, film post-production, which might have seen or solved some of these newly experienced "problems", which might've been caused by hardware choice(s) for example.
These IP addresses being released at some point, and making their way into something else is probably the reason I never got to fully run my mailserver from my basement. These companies are just massively giving IP addresses a bad reputation, messing them up for any other use and then abandoning them. I wonder what this would look like when plotted: AI (and other toxic crawling) companies slowly consuming the IPv4 address space? Ideally we'd forced them into some corner of the IPv6 space I guess. I mean robots.txt seems not to be of any help here.
The “Better Gradients” thing is dodgy.
OKLCH is a polar coordinate space. Hue is angle in this space. So to interpolate hue from one angle to another, to get from one side of a circle to the other, you go round the edge. This leads to extreme examples like the one shown:
You can also go round the circle the other way, which will take you via blue–aqua instead of via red–yellow: The gradient shown (in either case) is a good example of a way that perceptual colour spaces are really bad to work in: practically the entire way round the edge of the circle, it’s outside sRGB, in fact way outside of the colours humans can perceive. Perceptual colour spaces are really bad at handling the edges of gamuts, where slightly perturbing the values take you out of gamut.Accordingly, there are algorithms defined (yes, plural: not every application has agreed on the technique to use) to drag the colour back in-gamut, but it sacrifices the perceptual uniformity. The red in that gradient is way darker than the rest of it.
When you’re looking for better gradients, if you’re caring about perceptual uniformity (which frequently you shouldn’t, perceptual colour spaces are being massively overapplied), you should probably default to interpolating in Oklab instead, which takes a straight line from one side of the circle to the other—yes, through grey, if necessary.
And in this case, that gets you about as decent a magenta-to-lime gradient as you can hope for, not going via red and yellow, and not exhibiting the inappropriate darkening of sRGB interpolation (… though if I were hand-tuning such a gradient, I’d actually go a bit darker than Oklab does).During its beta period, Tailwind v4 tried shifting from sRGB to Oklch for gradient interpolation; by release, they’d decided Oklab was a safer default.
Also, isn't the way browsers interpolate colors in sRGB just a bug that I assume is retained for backwards compatibility? sRGB is a logarithmic encoding, you were never supposed to interpolate between colors directly in that encoding - the spec says you're suppose to convert to linear RGB first and do the interpolation there...
It's not a bug, its a property of the colour space. Which is partially tied to how the colour is represented (RGB). When doing linear interpolation through the RGB cube (for eg a gradient), you normally pick the shortest path. It just so happens that sometimes that path passes thorough some shade of gray as different colour components are scaled.
Usually you fix it by moving your point through a different colour space. Choice depends on your requirements and mediums you're working with (normally different types of light sources or screens).
I had to write a low level colour interpolation librar for a few interactive art projects, so I dipped a bit into this, but I'm no colour expert
No, sRGB refers to both a colour space and an encoding of that colour space. The encoding is non-linear to make best use of the 256 levels available per channel, but you were never supposed to interpolate sRGB by linearly interpolating the encoded components: you're supposed to apply the transfer function, perform the linear interpolation at higher precision, and then convert back down into the non-linear encoding.
Failure to do this conversion is what leads to the bad results when interpolating: going from red to green will still go through grey but it should go through a much lighter grey compared to what happens if you get the interpolation wrong.
I think GP is referring to the difference between "normal" (gamma-encoded) sRGB and linear sRGB. Though it's not logarithmic but a power law. In any case linear interpolation done in non-linear sRGB gives you intermediate colors that are darker than they should (though historically it's been so common in computer graphics that people are accustomed to it).
>During its beta period, Tailwind v4 tried shifting from sRGB to Oklch for gradient interpolation; by release, they’d decided Oklab was a safer default.
I recently implemented both, first I started with OKLab which turned out really well, the gradients you get from it are amazing and the usual color sets (analogous etc.) produce really pleasing sets.
However I quickly ran into the main problem with it, which is that fiddling with its Lightness, Chroma and Hue dials doesn't produce human understandable results. For example sometimes changing L or C induces a color shift, or for some given values changing L only gives midrange values that doesn't go up or down all the way.
I then implemented OKLCH on top of that, which was the way I assumed everyone was doing it. Just have it act as the controller for the human layer, then convert to OKLab for creating gradients etc. The article doesn't really go into it, but having OKLCH as the frontend controller fixes the LCH sliders such that they produce values that make sense to us humans, while still having the superior OKLab setup in the back.
This is super insightful, thank you! I wrote the article and will make changes to explain this better :)
IMO in pretty much all cases if the two colors at the end of your gradient are not already very close, you will always get the best results by manually specifying the colors at one or more steps between the two original colors.
Which brings me to point at the crux of the matter: avoid gradients between two dissimilar colors in the first place.
We already have CIE LAB as a standard that does the same thing... https://en.wikipedia.org/wiki/CIELAB_color_space
[EDIT] Ahh.. The W3C has already looked at this. https://www.w3.org/Graphics/Color/Workshop/slides/talk/lille...
For others, I'm sure parent knows: OKLCH is largely a bugfix for CILEAB. Both try to make a color space where even steps feel evenly spaced to a human. But CIELAB had procedural flaws in its creation.
See slide 19: https://www.w3.org/Graphics/Color/Workshop/slides/talk/lille... -- if you ask CIELAB to make "pure blue" (RGB 0 0 100%) become grayscale, the intermediate colors become purple to the human eye. The entire point of a perceptual color space is that that doesn't happen. OKLCH fixes that.
BTW, credit to Björn Ottosson, who basically side-projected a color space into the web standards and more: https://bottosson.github.io/posts/oklab/ ... folks like him are why we sometimes have nice things!
For anyone else copy pasting the gradients into dev tools to look at them: The second one is missing the # sign on the first color.
And yes, both oklch gradients look pretty weird while the oklab gradient looks nice (if you can accept it going through grey).
Can anyone share some images for those who don’t have dev tools to view them?
https://codepen.io/ItIsHappy/pen/dPYjyaV
Sorry, fixed.
But what really is a "color gradient"?
Isn't it any continuous function that starts at a specified color and ends at another specified color?
How then does one say that any gradient is good or bad?
Isn't the problem you are highlighting guaranteed to exist for any colorspace that defines colors outside of human perception?
A good gradient is one that takes a perceptually uniform, and typically perceptually shortest, path. The OKLCH gradient isn't perceptual uniform and appears to take unnecessary detours through other hues.
One could also argue that the detour through other hues is necessary in this case to avoid going through grey.
Gray is arguably just another color, it’s not clear why you’d want to avoid it. How is going via red and yellow better than going via gray? Varying hue is often perceived as a larger change than varying saturation or lightness. A path going through several distinct hues is visually less uniform than one going through gray once.
Is gray perceived as "just another color" or where all colors go when desaturated? I assumed the latter, which would explain why to avoid it if one isn't playing with saturation.
Think of fashion, of smartphone colors, pen and pencil colors and the like. Gray, white, black, are just color choices among all the available colors. A gray T-shirt isn’t a desaturated colored T-shirt. It’s its own color.
Color is weird like. Gray is “all the visible spectrum in equal proportions”, which is white… just less white than the whitest thing visible but more white than the darkest (blackest) thing visible.
It’s a “color” because it’s useful to describe such a thing. If you had monitor entirely filled with 50% white you’d call it white. Only by comparing it to something brighter do you call it gray. Brown is the same thing. In a dark room if you looked at a monitor filled with red and green pixels you’d call it orange. Only when you start adding in clues like whites and brighter colors would you call it brown.
Anyway, yes grey is a color. But it is not quite the same as other colors. Other colors occupy only parts of the visible electromagnetic spectrum. Whites are the whole thing.
There is actually several very good technology connections videos about this stuff. Color is very cool!
> Whites are the whole thing.
...with varying definitions of "whole". D65 white is almost blue when compared to A white. It stops being either “all the visible spectrum" or "in equal proportions” pretty quickly once you look closer at it.
Oh, I understand what you say. But in color spaces, isn't gray the "sink" towards which desaturated colors shift? This would make it a location to avoid (unless you're purposefully desaturating).
A grey shirt is a desaturated shirt. You cannot resaturate grey.
I think if you buy a tie-dye shirt or phone case and it comes out half grey, despite it being a valid color, most folks will be disappointed.
> A grey shirt is a desaturated shirt. You cannot resaturate grey.
Aren't these in direct conflict? If you can't resaturate it, that implies it's not desaturated.
> I think if you buy a tie-dye shirt or phone case and it comes out half grey, despite it being a valid color, most folks will be disappointed.
And if you buy a forest motif, people will be upset if it's pink. That's just doing a tie-dye wrong, not a rebuke of whether it's a color at all.
> Aren't these in direct conflict? If you can't resaturate it, that implies it's not desaturated.
Kinda. There's a singularity in the math. The problem is that hue is defined as an angle and saturation is defined as distance from the center, but there's no consistent way to define a direction for the origin. Black and white have the same problem because they're also desaturated.
> And if you buy a forest motif, people will be upset if it's pink. That's just doing a tie-dye wrong, not a rebuke of whether it's a color at all.
I'm not arguing that it's not a color, just that it doesn't belong in all gradients!
Of course it doesn't belong in all gradients. It would only be in gradients that go from near-opposite colors. Or if you mean pure gray it would only be in gradients between exact opposite colors, and there are no good options for such a gradient.
I mention tie-dye because it feels like a quintessential example of a color gradient. I think it's perfectly reasonable to ask for a blue and orange tie-dye shirt and perfectly reasonable to not want grey colors simply because they're on opposite sides. I could see white in between, I could even see black, or I could see purple and red or cyan and yellow. I don't think there's a universally right answer here!
Someone asking for those colors doesn't actually want a gradient with two anchor points. So yes there are many answers but because it's not a quintessential example of a gradient.
> Someone asking for those colors doesn't actually want a gradient with two anchor points.
I thought the same until I googled "blue and orange tie-dye." I'll be honest, more white and black than I expected!
> So yes there are many answers but because it's not a quintessential example of a gradient.
We may have to agree to disagree that tie-dye isn't a quintessential example of a gradient. Would you argue that rainbows aren't either?
> I thought the same until I googled "blue and orange tie-dye." I'll be honest, more white and black than I expected!
Putting white or black in between adds another anchor point.
And looking more around examples of blue and orange tie dye, most aren't really gradients overall, they have big splotches of solid color with small gaps or overlaps in between, and at least half the time the gaps and overlaps don't even have a gradient inside them.
> We may have to agree to disagree that tie-dye isn't a quintessential example of a gradient. Would you argue that rainbows aren't either?
Hmm. How about this. I would say a rainbow is not a gradient between two colors, and the color space discussion is about a gradient between two colors. The exact border of "quintessential" is not something I really want to spend too much time on.
In my mind a gradient is simply a smooth transition between colors with no universally agreed upon definition. The choice of specific curve through colorspace is rather arbitrary. It seems perfectly reasonable to want to include grey and perfectly reasonable to want to avoid it.
Let's say you continuously change wavelength of a laser from blue (~480nm) to red (~630nm), you are going through green, not through gray. If in your use case going through gray makes sense, that's ok, there may be many paths from one color to another.
In general people don't really think of color in terms of the spectral progression (or the hue wheel), and I don't think that most people intuitively expect a gradient between two colors to pass through another "unrelated" primary or secondary color. The point is somewhat moot though, given that such gradients (like yellow to blue or red to green) are very unnatural anyway.
I disagree somewhat. Color mixing just isn't particularly intuitive. It's not the most intuitive to get a third hue, but that doesn't justify grey (which has an undefined hue). I do think most people are quite comfortable with the fact that between blue and yellow exists green, but is it a saturated green or a desaturated green? Additive and subtractive color mixing behave very differently here.
It's funny and a bit sad because we just went througha decades-long effort to migrate away from jet/rainbow gradients to vik/batlow/bi-hue gradients, and now rainbow is forcing its way back.
https://theconversation.com/how-rainbow-colour-maps-can-dist...
https://www.poynter.org/archive/2013/why-rainbow-colors-aren...
Honestly I suspect this is largely a non issue. I have never made a gradient that goes through more than 2 different color (by some vague measure of different) without adding an additional stop. If I wanted to go through yellow and green to get to blue, I would add a stop at yellow and another at green, and I suspect most developers would do the same.
Shine a red and a green light near each other on a wall — what does the transition look like?
There's no transition, this is color mixing, or overlay in case of light.
Is that not a transition through the color mixing (or overlay). I'm assuming the light sort of tails off as you leave the area of one color and head to the other (and the other color comes on with more intensity then).
I suppose that's different with light than some analog with pigments? (Two dabs of color set apart, a brush perhaps used to blend them as continuously as is possible.)
Your light thought experiment would produce a color gradient via additive color mixing.
A magenta to green gradient would then go through white rather than grey. A subtractive magenta-green gradient would go through black. Not sure what physical setup would produce the latter gradient. But the standard RGB (or OKLAB) gradient goes through grey rather than white or black. This type of gradient is physically created by dithering: Dithering a gradient from magenta to green, by just using these two base colors, would produce a perceptual grey in the middle. This type of color mixing is otherwise better known as alpha blending.
It depends on how you think about your spread. If, as someone else said, you're trying to represent a tunable laser going from red to blue, going through gray is completely wrong. That is not what a laser will do, ever. It will always be a fully saturated color.
So, depending on what you're doing, you want different things. You may want to view your color space as an RGB cube, and go through gray. Or you may want to view your color space as something more like HLS or OKLCH, and not go through gray.
Gray is arguably not just another color; I don't know about English but in German you have 'bunte' and 'unbunte' colors; 'unbunte' colors are white, black, and the grays in between
It's an ugly color. Saturation makes stuff pop; this is often desirable. This is why I think it's important to have both polar (OKLCH) and rectilinear (Oklab) gradients.
Let's say neither going through gray nor through two different hues looks particularly great. It's pick your poison.
> Gray is arguably just another color
Only if you're working with additive color.
With substractive, grey is just a darker (or dimmer) white.
Interesting. In nature, I suppose I am most aware of a gradient from a saturated azure sky above to a much whiter sky on the horizon. This would seem to be a trivial saturation gradient.
For a spot color (from a gel covering a light) the light diffuses further from the center of the projected light — two spot colors (with different gels) then, next to each other, would give a kind of gradient from one color to the next as you walk a line from the center of one light to the other.
I wonder what the closest analog to this is algorithmically?
I guess where I am going with this is: is there precedent in nature as to how gradients are supposed to work (and therefore an analog which we should try to model) or are we going strictly on how the human eye perceives color and what algorithm we think "looks" right?
Edit: The article was updated. Ignore me.
> you should probably default to interpolating in Oklab instead
The article says as much. Quoting:
> This can be a double edged sword. While some gradients might look smoother, you might also see colors that you've never defined. This is because hue in OKLCH is circular and gradients can take unexpected detours.
> To avoid this, many tools use OKLAB for gradients, which interpolates in a straight line and gives more consistent results.
I was going to point that out too until I realized that the author updated the article based on the parent comment!
https://news.ycombinator.com/item?id=45013291
Ha! Well spotted.
Making a gradient from two colours on opposite sides of the spectrum is a bit of a pathological case. There's no obvious answer what it "should" look like, and also no good reason you'd really need to do this. If you're using a gradient as a design element, you'd pick your own midpoints.
Very interesting. Is this just a limitation of our current hardware? How much of this problem would still exist if everyone had a wider gamut monitor, say full DCI-P3? That still doesn't cover the full gamut of Oklch, but would it make the problem practically disappear?
No. We’re talking about colours way beyond the ranges of human perception.
For this specific gradient, see https://oklch.com/#0.7017,0.3225,328.36,100 and https://oklch.com/#0.86644,0.294827,142.4953,100, and look at the Chroma panel, see how far out of our screen gamuts they are (even tick “Show Rec2020”, which adds a lot of chroma around blue–green and magenta–red), and try to imagine the colours between the lime and magenta (in either direction). The red direction is probably the easier to reason about: there’s just no such colour as a light, bright red. You can have bright or light, but not both. (Its 3D view can also be useful to visualise these things: you’re building a straight-line bridge between two peaks, and there’s a chasm in between.)
I don't get it, why am I seeing the "out of gamut" colors if my sRGB monitor is unable to display them? Would the charts look different on a P3 monitor?
edit: Also, you mentioned the colors "beyond the ranges of human perception" but I don't think there is any such limitation here, the bottleneck is the hardware (computer monitors).
It’s squashing the range of the colours down to simulate it.
I don't understand why HN sometimes responds aggressively to an honest, puzzled question. It's as if being wrong (or confused) was a sin here, sometimes.
I thought yours was an honest question that warrants an answer (which thankfully Chris answered).
It was an honest question, thank you.
Wow, I never thought about bright light red when thinking of undisplayable colors. It makes a lot of intuitive sense, thanks!
But once an algorithm to drag the colours back in-gamut was applied, would the lost perceptual uniformity still be a problem practically speaking, with DCI-P3 monitors?
Yes. I repeat: these colours are way outside gamut. Not just a little bit. P3 helps a little bit, Rec.2020 would help a fair bit more, but you’re still asking for a yellow that is about twice as vibrant as is possible.
The underlying problem is that the color space humans can see doesn’t have nice uniform linear boundaries. The larger your color space, the more relevant that issue actually becomes.
RGB is just allways worst OKLCH usually pretty, which is all I want from gradients most of the time.
I had claude build me a comparison (not sure why 2x the same HSL one) https://i.imgur.com/uziQibR.png
Also super hard in RGB: https://jsfiddle.net/nhgvzm5p/2/ it's just a 2 color OKLCH gradient:
That gradient looks terrible, very bad colour banding, because you’re starting and ending at points that are way out of gamut, and the technique used to bring it in isn’t smooth. For a gradient like that, you probably want at least five points.
That is the biggest problem with these colour spaces: the edges are unclear, and overflowing them has bad effects.
you think I can get the same OKLCH style colors but without banding?
if I sample 5 colors and throw them in as rgb?
the 3 color rgb one has very similar banding
my biggest problems with OKLCH:
- how to easily add "warmth". you can't just add red+green - no good tools for it (e.g. a nice gradient picker ui that lets me specify if I want to allow running out of bounds of teh color space and clip a few colors at max saturation)
> The red in that gradient is way darker than the rest of it.
It doesn't look significantly darker to me.
Great post!
Also check out oklch.com, I found it useful for building an intuition. Some stumbling blocks are that hues aren’t the same as HSL hues, and max chroma is different depending on hue and lightness. This isn’t a bug, but a reflection of human eyes and computer screens; the alternative, as in HSL, is a consistent max but inconsistent meaning.
Another very cool thing about CSS’s OKLCH is it’s a formula, so you can write things like oklch(from var(--accent) calc(l + .1) c h). Do note, though, that you’ll need either some color theory or fiddling to figure out your formulas, my programmer’s intuition told me lies like “a shadow is just a lightness change, not a hue change”.
Also, OKLCH gradients aren’t objectively best, they’re consistently colorful. When used with similar hues, not like the article’s example, they can look very nice, but it’s not realistic; if your goal is how light mixes, then you actually want XYZ. More: https://developer.mozilla.org/en-US/docs/Web/CSS/color_value....
Also, fun fact: the “ok” is actually just the word “ok”. The implication being that LCH was not OK, it had some bugs.
> Another very cool thing about CSS’s OKLCH is it’s a formula
While it’s more useful for a perceptual color space, relative colors are supported for all CSS color spaces e.g.
OKLCH plus relative colors let me seriously reduce the amount of hardcoded colors from my style sheet:
https://github.com/hazelgrove/hazel/blob/dev/src/web/www/sty...
Aside from a few criticisms that others have already raised I think this is quite a nice introduction to OKLCH and how to use them in CSS.
With that out of the way, I'd like to go on a tangent here: can anyone explain the modern trend of not including publishing dates in blog articles? It stood out to me here in particular because the opening sentence said that "OKLCH is a newer color model" and the "newer" part of that sentence will get dated quicker than you think. The main site does mention a date, but limits it to "August 2025" so this seems like a conscious choice and I just don't get it.
[0] https://jakub.kr/
> can anyone explain the modern trend of not including publishing dates in blog articles?
In such cases, I usually try to see if the `Last-Modified` header served with the HTML document over HTTP, can be useful, but I conclude that often the same people who don't bother with dating their content -- you'd think they'd understand where the word _blog_ comes from, as in "[web]-log" where timestamps are paramount -- these same people don't know or care how HTTP works. Hint: the `Last-Modified` is the last modification time of the _resource_, in this case the actual HTML document. Just because your "backend" re-rendered the content because you didn't bother with setting up your server caching correctly, doesn't mean you should pretend it's a brand new content every day (which https://jakub.kr/components/oklch-colors does, unfortunately, so you won't know the timestamp from HTTP).
I would imagine this is rather to whatever "blog engine" is used instead of the conscious choice of the author (even if they knew what they desire and what would qork better, it might not be their priority).
I can't explain it, but undated articles are a serious problem. I don't know whether it's a modern trend ... how can one tell in the absence of dates? I've seen plenty of undated content that appears to be old.
On some blogs I can only tell the timeframe of the content from the timestamps on the comments ... but many blogs like the OP's don't support comments. I'm not likely to revisit them. (The blurb on the OP's main page is ironic ... rather than obsessing over the smallest details I see obsession over esthetics to the detriment of functionality.)
SEO to protect old content from being demoted. It is annoying.
I'm surprised they don't punish undated articles then
Blame Google and SEO
I found this to be a good article on the subject:
https://evilmartians.com/chronicles/oklch-in-css-why-quit-rg...
Along with their picker / converter here:
https://oklch.com/
Discussed on Hacker News here:
https://news.ycombinator.com/item?id=43073819 (6 months ago, 30 comments)
> In the example above, you can see that the OKLCH colors maintain consistent blueness across all of the shades, while in the HSL example, the lighter shades drift to purple and the darker ones muddy out towards grayish.
There is a very clear shift towards green in the OKLCH lightness value change example, enormously more so than any purple vibe in the HSL example.
Clearly being able to select colours of the same perceptual intensity has value, but some of the claims here as to the benefits are exaggerated.
You can see why by looking at the Hue chart for this color:
https://oklch.com/#0.7684,0.1754,218.1,100
To increase brightness past the limit of the Hue band for the color, the rendered output color on a display shifts cyan due to the limited brightness range of a saturated blue in the Display P3 color space. OKLCH is, when varying brightness along a gradient, Saturation-invariant rather than Hue-invariant; whether that effect is desirable is a matter of aesthetic preference, but after decades of Hue-invariant desaturated web color, it’s certainly refreshing to have a choice about which compromised invariance to take.
https://news.ycombinator.com/item?id=44588388
Science recently invented a much-deeper blue LED than we have now, so I expect in a decade or two, whatever ends up succeeding Display P3 will be much more able to represent that gradient without cyan-shift, and all of the years of OKLCH gradients created before that time will end up showing a more accurate blue gradient with only the colorspace change. In the meantime? Do whatever’s aesthetically pleasing; there is no Right Answer in design :)
ps. One could argue that a post-OKLCH colorspace should not accept the binary decision of Hue or Saturation invariance, and instead should be Saturation-invariant to the display’s native limit and then transition smoothly to Hue-invariance at that threshold. I believe that’s a Difficult Problem in color profile specification terms, since it isn’t just pre-calculating the changeover threshold for all monitors (not to mention, do you change blue sooner or same as red, etc) but it’ll be a while longer before I’m versed enough in ICCv4 to explain that perception. It sure would make for an interesting experimental DisplayCAL target, though!
> You can see why by looking at the Hue chart for this color
This misses the point: the example claims the hue isn't shifting, when it very clearly is. It's not a question of why.
The hue isn’t shifting in OKLCH at all; also, it’s definitely shifting when OKLCH is rendered to Display P3 or sRGB. This is normal and expected behavior for colorspace gradients when rendered to device profiles? But I suspect I’m too close to the problem to see what’s not explained properly, apologies.
No, it's not normal or expected for hue to change when rendering to a limited gamut.
It's normal and expected for saturation to change. And for brightness to get clipped. But not for hue to change.
That's the critique of OKLCH here, that changing hue is a bizarre and undesirable choice.
Your viewpoint of there being one true way of spectrum gradation under restricted device domains is not universally agreed upon; neither among designers, nor among the ‘normal’ population. No other way is the one true way, either! What works well for a PC sRGB display will be drab and lifeless on a laser cinema projection systems. Printers have faced this problem for centuries and innovated to use glass (long ago) and brushed-metal prints (more recently) as a way to regain control of luminosity independent of saturation and to express their design in less restrictive ways. The only ‘normal’ in this scenario is the shared agreements we make, and the primacy of sRGB’s desaturated brights as the sole exclusive agreement is ending.
(Since this reminded me of it, a random pro tip: For those using macOS Terminal.app, you can redefine the 16 ANSI colors using the full P3 colorspace, so long as you use the full GUI color picker rather than the sRGB-limited #rrggbb entry method. Access to improved saturation helps the eye distinguish different shades in the dim and bright color sets more effectively without having to alter their brightness. It won’t improve the limitations of ANSI color as a whole — the insistence on Luminosity = f(R,G,B) is baked into everyone’s assumptions quite deeply thanks to sRGB! — but it does at least mean you can have seven equidistant and non-desaturated, non-sRGB colors at two levels of brightness for syntax highlighting and other typical 16-color uses.)
There’s no green shift at all in that example on my display. Could your calibration be off?
It's practically cyan, which is half way to green, not a lighter version of the blue to the left. This is on a MBP built in display.
This totally has uses but it is not, as claimed, "there is no hue or saturation drift" given the hue has shifted so much.
There certainly is ... run a color picker over it.
I opened the macOS Digital Color Meter and set it to "native values" mode. The second-to-last OKLCH swatch has a green component of 202, and the last has a green component of 226. The corresponding values in the HSL swatches are 203 and 227.
Basically no difference at all.
> The corresponding values in the HSL swatches are 203 and 227.
That is a gigantic difference. Those are totally different hues. Which are, of course, exactly the difference we're seeing.
I'm saying HSL has the exact same shift as OKLCH. And neither is visibly green to me.
It's visibly cyan, isn't it? It's maybe not an intuitive "green" hue (depending on your linguistic culture), but it's clearly different from all the other colors on that chart.
Agreed. The hue changes completely from blue to cyan.
If that's a correct implementation of OKLCH, then it's not something I would ever touch. Something seems to be deeply wrong with however they're calculating hue.
HSL/HSV have issues with perceptual lightness. But not with hues. The hue is constant and doesn't need any correction depending on saturation or lightness.
I think you do usually want to rotate the hue a bit when changing the lightness though. It’s a difficult thing to get right and one of the reasons the tailwind builtin colour palettes are so useful.
You don't. That's not something graphic designers ever do as compensation for perceptual uniformity.
I looked into it a bit more, and it turns out it's a result of OKLCH easily producing colors out of gamut, and then choosing to sacrifice hue accuracy for better saturation accuracy.
That's a fundamental design flaw if you ask me. Changing hue is completely unacceptable in my book.
In "Refactoring UI" [1] (by the creators of tailwind) they recommend when designing your shades for a single base colour:
> Since different hues have a different perceived brightness, another way you can change the brightness of a color is by rotating its hue.
> To make a color lighter, rotate the hue towards the nearest bright hue — 60°, 180°, or 300°.
> To make a color darker, rotate the hue towards the nearest dark hue — 0°, 120°, or 240°.
> This can be really useful when trying to create a palette for a light color like yellow. By gradually rotating the hue towards more of an orange as you decrease the lightness, the darker shades will feel warm and rich instead of dull and brown
You could argue whether this is "perceptual uniformity" or something else, but the fact is that to create a realistically useful colour palette with a bunch of shades, you definitely cannot simply use HSL, keep the hue constant, adjust S/L. It's not that easy (and OKLCH doesn't make it that easy either).
1. https://www.refactoringui.com/
sRGB is already not perceptually uniform. These hue changes already happen. Just because the H value in HSL/HSV doesn't change doesn't mean there's no perceptual hue shift when adjusting lightness/value.
I don't know what you're talking about -- that isn't true.
There is absolutely no perceptual hue shift in the HSL/HSV models depending on saturation and lightness/value, or when they get translated into sRGB. That's the entire point of HSL/HSV, to isolate hue and hold it constant.
HSL/HSV are not perceptually uniform in terms of brightness when hue is changed, or even brightness linearly. But hue is hue. Perceived hue does not change based on brightness or saturation.
There most definitely is perceptual hue shift in HSL (and HSV); it's illustrated quite well at [0](The blog of the creator of OKLab), particularly in [1], an image showing S and L axes while leaving H fixed.
[0]https://bottosson.github.io/posts/colorpicker/
[1]https://bottosson.github.io/img/colorpicker/hsl_blue.png
Well I'll be damned, you're right -- I'm playing with it in Photoshop now, and it seems to be exclusive to hue values of 233-270, in the transition from blue to purple, and nowhere else. Matches what [0] says -- "This is particularly obvious for deep blue and purple colors."
So first, thank you for the correction. It's fantastic to learn something new. And second, do you have any idea why the OKLCH example on the page is so atrociously bad? The way blue changes to cyan is even worse than the HSL/HSV difference of blue-purple. It's like the cure is worse than the disease. If they were so concerned with hue fidelity in the first place, I'm surprised they wound up producing an end result just as bad.
I don't know much about the science of colors and I imagine this is going to be very subjective but I would at "worst" describe the rightmost OKLCH color as blue-green (but probably just "light blue"). Meanwhile the two rightmost HSL colors I would not describe as blue at all. Second from right I would call "light purple" and the rightmost honestly looks grey to me (which is weird because the caption says the darker HSL values "muddy out towards greyish" but the leftmost values for OKLCH and HSL both look pretty blue to me).
Also if I use the macOS app "Digital Color Meter" I get essentially the same green value for the rightmost OKLCH and HSL colors (226 and 227 for "display native values" and 228 and 227 for sRGB).
OKLCH: a color model based on OKLab (a perceptually uniform color space) where you control Lightness, Chroma (saturation), and Hue.
"OK" because "it does an ok job" according to its creater Björn Ottosson.
He’s Swedish, so I bet OK is actually short for “Ottossons kulör” but he’s just being modest.
In the spirit of "Oll Korrekt", "Otto's Kolors"?
How do you pronounce it, btw? "Oklich"? "okay L.C.H."?
Ok Lunch :)
https://dillonshook.com/how-do-you-pronounce-oklch/
Lich is an old word for a corpse (or in D&D mythology an undead magician).
An okay lich is like a chill corpse, maybe?
Was more thinking of a single word like "Oxford", but that works as well!
Wherever you're working with colors and text/emblems, please also consider contrast and legibility: <https://apcacontrast.com/>
While the above site is great for measuring with a modern contrast algorithm (it’s the current algorithm for the yet-to-be-released WCAG 3 accessibility standards), it’s worth bearing in mind that the WCAG 2 algorithm is somewhat different, and a legal requirement in many markets / industries. You can check your colours against that with a tool like https://www.siegemedia.com/contrast-ratio, although there are many more.
Any reference to APCA has been removed from the WCAG 3 drafts in 2023 (see https://github.com/w3c/silver/commit/d5b364de1004d76caa7ddc4...).
I am not sure what the status is.
Oh, interesting, I’d missed that. Good info, thanks!
You can pick colors that pass both APCA and WCAG contrast checks though so it's not a problem to use APCA recommendations now.
I find APCA is a little stricter than WCAG for light themes, and APCA is much stricter than WCAG for dark themes, to the point where you really shouldn't use WCAG for dark themes. So most of the time APCA is giving you stricter contrast that easily pass WCAG also.
I keep seeing mentions that APCA will let you finally use e.g. white on orange, or white on vibrant blue that pass APCA but fail on WCAG, but my feeling is there's not a lot of examples like this and most of these pairings only have okay contrast anyway, not great contrast, so it's not ideal to be stuck with WCAG's false negatives but not that big of a deal.
If your colours have enough contrast to pass them both then of course that’s fine!
I only bring it up because I had a situation last week where the better APCA was giving results for both white-on-colour and #111-on-colour as suitable for headline copy under WCAG3, but #111-on-colour was 7.5:1 and white-on-colour was 2.5:1 under WCAG2, hence we could only use one of them legally.
> I only bring it up because I had a situation last week where the better APCA was giving results for both white-on-colour and #111-on-colour as suitable for headline copy under WCAG3, but #111-on-colour was 7.5:1 and white-on-colour was 2.5:1 under WCAG2, hence we could only use one of them legally.
Yeah I understand, would you agree this is fairly rare when using APCA though?
I've had the opposite where the brand guide was suggesting we use a light on dark combo that passed WCAG2, yet it failed APCA, and worst of all clearly had poor contrast just by looking at it. Yet, some people will still go with it because WCAG2 gave it the okay haha.
Rare, yes. Checking with both is definitely recommended!
Maybe you've seen this but there's also https://github.com/Myndex/bridge-pca that does the "this color pair passes both APCA and WCAG2?" check in one pass.
As per discussion of this new OKLCH idea in TFA - Are we even sure we have great formulas for measuring/defining contrast in the first place? Do you agree / disagree with any of the counterexamples over at: https://github.com/tattoy-org/contrast-experiments
I'm not following. These examples are using the WCAG2 contrast algorithm which is well known to be flawed for people interested in this stuff, especially for dark themes so there should be lots of bad examples here? APCA is supposed to improve on this (see the example graphic comparing WCAG2 and APCA): https://git.apcacontrast.com/documentation/WhyAPCA.html
> But as @c-blake has rightly pointed out, this doesn't take into account the ratio of visible background pixels to foreground pixels. For example the contrast required for a single fullstop character, ".", is goting to be diffrent from a capital, "B".
So APCA includes more guidance on font weight and font size for more contexts (e.g. headings, body text, shorter text, copyright notices), but it's still going to be an approximation for edge cases like displaying a single fullstop character. If this case is common, you'd want to increase the contrast value instead of going with the minimum passing value, so the contrast algorithms can still help you.
There's a tradeoff with having guidelines that are very accurate (e.g. a contrast algorithm that counts pixels) vs simpler to follow (e.g. recommended font weight and size). People already find WCAG2 hard to follow as it is.
I don't think you & I have much disagreement here as I like the way you write about approximations and edge cases and things involving human judgement calls and "both not either" kinds of testing. The WhyAPCA document you link to also includes language to such effect with sliding scales over regions & such. Me - I'm mostly asking questions not offering answers. That said, to correct the record..
>These examples are using the WCAG2 contrast algorithm which is well known
Only one of the 4 tables shown is the thing you say is the known-to-be-flawed WCAG2 one. Some counterxamples are listed for all 4 formulas, though, 2 of which use the CIE Lightness (which, sure, is probably different, but I believe the CIE L is what APCA is based upon - in spite of so..many..words on their doc pages they often just say "lightness").
------------------------
Another point of those 4 tables, perhaps more clear when looking at the python script, is whether "numerical ratio" vs abs(difference) is better. It seems to me that color space designers, like this OKLCH, are going after "perceptual linearity" which suggests abs(diff) is far more appropriate than a "ratio" which has "near zero" troubles (and zero & one are downright seductive numbers for perceptual lightness scales).
I certainly should learn more about it, but various "click through" APCA things I've seen seem to speak in ratio terms like "10 times the contrast" (though admittedly that only assumes some scale for contrast not that it's formulated as a ratio - it's just suggestive). So, I should probably look more into it before actually offering a critique, but it still has the feeling of "cross purposes" - using some color space axis designed for [0,1] linearity differences instead for ratios within that axis. When I tried using the WCAG2 one I was kind of stunned how sensitive everything was to what should have been a kind of "arbitrary adjustment" to handle near-zero.
I might wonder what designers of color spaces actually have to say about this ratio vs. difference issue if you know of any articles. You seem knowledgeable. The spaces seem literally designed for differences to me.
There is no real difference between ratio and difference. It is just scaled with a logarithm. See https://blog.ce9e.org/posts/2022-09-10-contrast-algorithms/ for details.
Your link itself admits the 0.05 makes it a different formula. Both Y and L* go to zero for hard black which is a very common color (the most common for me) and would be infinite with black in there. I disagree this is all "not real".
The 2x2 table in that contrast experiments link I sent enumerates some differences along the edge cases { even with just |diff|s. }. Just empirically if you change that 0.05 to 0.02 or 0.10 things change "a lot" in terms of all the edge cases. You can try fiddling with running that Python script yourself and see.
Also, I believe the project of an actual "contrast measurement" - not merely threshold checking - is a worthy goal. I think it would be good to be able to say how bad, and for that the specific monotonic transformation absolutely matters, and again, I expect the color space designer people have opinions on this very worth listening to. I think they are targeting differences in the numbers being the most meaningful thing.
All that said, I did like your George Box quote. :-) I just don't think dismissing the problem is a great solution here. I'm not sure there is a great solution. But you & anyone are always free to find any problem uninteresting. I mean, you could also find all the color space distinctions of TFA similarly "no real difference".
On the comparison between Color spaces, it's weird, my monitor from 2008 does show a difference between the Display-P3 and the sRGB purple colors, yet I didn't think it'd have such a big color range. Is there some color conversion at the browser or OS-level? (my distro/desktop enables colormgr by default).
It’s just completely wrong.
The first uses oklch(0.65 0.20 300), comfortably inside sRGB, not even at the boundary. The second uses oklch(0.65 0.28 300), which is well outside P3 and even Rec.2020.
The smallest fix would be to make the second one oklch(0.65 0.2399 300) to bring it inside P3 so the demo doesn’t get slightly warped if Rec.2020-capable (not really necessary, but preferable, I’d say), and the first #a95eff (oklch(0.6447 0.2297 301.67)) which is CSS’s fallback.
But purple is also pretty much the worst choice for such a demo—P3 adds the least to sRGB around there, so the difference will be smallest. A better choice is red or green.
So a better pair would be oklch(0.65 0.2977284 28) on the right (a bright red at the very edge of the P3 gamut, well outside sRGB) and #f00 on the left (the sRGB value CSS will map it to if out of gamut).
Sort of off topic questions, do we have any upcoming colour space beyond BT2020, now that we soon have monitor that reach 100% BT2020. I did some search and it doesn't seems to be any.
For any really bigger color space, you would have to use more than 3 primary colors, which would increase a lot the cost.
Moving the monochromatic BT.2020 colors from 630 nm, 532 nm and 467 nm could get a little increase in color space coverage, but at the expense of a lower efficiency in power consumption to brightness conversion. 467 nm is not a very pure blue, but the sensitivity of the eye drops very quickly in the blue region, so a better blue would require much more power. Similarly, though not so pronounced, for a different green.
Moreover, in the green region there is a gap, both for lasers and for LEDs, where the available devices have low efficiencies for converting electrical power to light, so changing the frequency of the primary green color would have to take that into account too.
In conclusion, I believe that the BT.2020 (actually BT.2100) color space is close to the best that can be done in displays of reasonable price and energy efficiency.
A true coverage of 100% of the BT.2100 color space can be realized only with laser projectors. Any display with LEDs or quantum dots will never have really monochromatic primary colors, though a coverage of significantly more than 90% of the BT.2100 color space is not too difficult. However, the advertised percentage of the color space may be misleading, because it varies depending on the kind of color space used for computations. A coverage percentage computed in OKlab would be more informative than a percentage computed in the XYZ color space.
> For any really bigger color space, you would have to use more than 3 primary colors, which would increase a lot the cost.
Unless you want to make displays for the bees and birds (and the tiny alleged minority of human tetrachromats) that seems rather pointless. People with three color receptors are your customers, so that's driving the market.
I rather predict, future displays will further improve on contrast, including very bright (brilliant) sparks. Imagine an iPhone glittering like gold or diamonds ...
This has nothing to do with tetrachromatism.
The border of the color space corresponding to monochromatic colors is convex, so any triangle inscribed in that curve border will leave parts of the color space that cannot be reproduced on a display.
The convexity of the border means that if you compute the 3 coefficients of RGB colors that match a desired color, there will always be some colors that need one negative coefficient, regardless of the choice for the RGB primary colors. On any display, it is impossible to realize a negative brightness of a color, so on a RGB display there will always be some colors whose hue and brightness can be reproduced, but their saturation cannot be reproduced.
The only way to make smaller the parts of the color space that cannot be reproduced is to take more points on the monochromatic border, replacing the triangle of reproducible colors with a polygon that fits more closely the curved border.
The entire color space perceived by humans could be reproduced on a display only with tunable lasers, not with fixed-frequency primary colors. One could use fixed-frequency primary colors only if they would stimulate directly the photoreceptors in the eye, to enable workarounds for the overlapping filter characteristics of the cones and for the signal processing done in the retina.
That's not the issue. Take pure blue wavelengths as an example. They also activate your green cones a little. Increasing the frequency activates the blue cones less and the green cones much less, yielding a higher ratio of blue to green activation, and a new color (violet) that you can't represent with mixed color output exactly aligning with mode receptor wavelengths.
>Any display with LEDs or quantum dots will never have really monochromatic primary colors
I was referring to the new RGB LED. From what I have read so far seems to be doing far better than LED or quantum dots.
But I guess we will have to settle with BT2100 then.
This should be fixed now as well!
Good, much improved.
One last thing:
> This way the browser uses OKLCH colors if they are supported, otherwise it falls back to sRGB.
This wording suggests it’s about gamuts, but it’s actually about syntax. It will use the oklch() if that syntax is supported, and then the OKLCH value may be within sRGB or may be in another gamut the screen is using or may need to be mapped back to the screen’s gamut. Whereas #rgb values are inherently limited to sRGB, the baseline.
I tried working with it but had to give it up for practical purposes. Whereas the focus with HSL is on the Lightness part and the Saturation is made to fit, OKHCL does it differently. It pushes the Chroma part to it's technical limits and abuses the Hue to make it fit, but we just do not understand Chroma intuitively. I am waiting for OKHSL where the adjustments will bu much smaller and do not lead to absurd changes in intent. I already had a discussion about it somewhere else (https://www.reddit.com/r/css/comments/1jv5f0r/hue_is_an_issu...)
My mind immediately translated OKLCH into "Oklachroma".
For historical "neat" factor, here's the original blog post that introduced the color space:
https://bottosson.github.io/posts/oklab/
Why is there no documented formula to convert to from this color space? A quick google and the best I could find is this Gist[0]. Searching for Oklab has a Wikipedia page[1].
[0] https://gist.github.com/dkaraush/65d19d61396f5f3cd8ba7d1b4b3...
[1] https://en.wikipedia.org/wiki/Oklab_color_space
It looks to me that all the "magic" is in the matrices used for conversion between Oklab and sRGB. The final conversion between Oklab and Oklch is trivial, and is documented in your linked Wikipedia article.
OKLCh is the same space as OKLab, it's just polar coordinates versus rectangular coordinates.
That gradient example is hilarious.
With RGB you order green salad you get green salad.
With OKLCH you order green salad you get beet soup.
Yes ... see chrismorgan's comment on it up top.
Nice post. OKLCH is quite handy but for writing colors in CSS I hope eventually we’ll get some form of OKHSL/OKHSV[1] so users don’t need to worry about gamut boundaries.
[1] https://bottosson.github.io/posts/colorpicker/
There is a youtuber (Gneiss Name) making educational content through the medium of Minecraft. He's made one on OKLab as well: https://youtu.be/nJlZT5AE9zY
What an absolutely fascinating channel! Thanks for the link
I've not touched oklch, but I've played with oklab gradients a fair amount.
How do they (oklch & oklab) compare for different uses?
oklch uses the oklab color space.
The oklch color space is polar: it’s a cylindrical transformation of the oklab cartesian color space.
That's quite misleading. The parent commenter was asking about gradient (interpolation between colors). Gradients look completely different in oklch and oklab.
Well yes, it's a different coorsinate system, so gradients would look different. It is still the same color space, but I agree I could have worded that better.
Does anyone know how this is different to the Munsell color space, which is also perceptually uniform?
Edit: I would imagine that the only way to definine a perceptually uniform color space is by tons of user testing. This is how Munsell developed his color space… specifically presenting test subjects with pairs of identical and near-identical color swatches and asking if they could tell the difference.
In this way, pairwise comparisom of similararity became the bedrock of color perception science.
The Munsell color system isn't really intended for displays, rather it's a collection of pigments, similar to Pantone. The transforms can get a bit weird (for example, since the swatches are discrete, there's no defined way to get intermediate colors). Munsell's ideas, particularly the axes of hue, value, and chroma, have absolutely influenced modern color spaces and are very much on display in the OKLCH space.
Oklch is open source and part of the web standard, Munsell colors probably needs a licence to be used ?
My understanding is that it's the same with higher resolution.
Really happy about oklch. You do have to learn the hue numbers, but once you do, everything is more intuitive.
The best axis for Lightness in my opinion is still the Gray-Scale (as used back in the day for black/white/grayscale TVs).
The newer CIE colorspaces (CIECAM02 CIECAM16) seem to address the effect, that color-perception goes wild if you change background and illumination. Oklab seems to only make some fixed choice about how to include the chromatic part to lightness. I'm not so sure, how this definition of lightness is any better than grayscale (from 1931).
Creator of OKLCH on OKLCH:
https://bottosson.github.io/posts/oklab/
Seems nice. But how to pronounce it?
That's one reason to prefer Oklab ;)
With great difficulty.
Like "okay lock" I would guess.
o k l c h
"Oh, clutch"?
> The way gradients work in OKLCH is pretty different compared to sRGB. In sRGB, gradients are calculated in red, green, and blue values, which often leads to muddy midpoints and uneven brightness.
I always understood those “muddy midpoints” as a failure to properly gamma correct the interpolation between two (s)RGB colors. Is that happening here, or is the mud coming from something else?
Grays run along a diagonal axis of the RGB cube after stripping gamma off. A straight line through the cube will brush by it. This is enhanced when transitioning from a primary (green) to an opposite corner (magenta).
I added oklab to emacs's color module. I initially intended to use it to make better procedural themes, but I haven't gotten to that yet. In any case, emacs version 30 has color-oklab-to-xyz and color-xyz-to-oklab functions that work with the other functions in emacs's color module to convert to/from oklab colors.
"In the example above, you can see that the OKLCH colors maintain consistent blueness across all of the shades, while in the HSL example, the lighter shades drift to purple and the darker ones muddy out towards grayish."
The OKLCH lighter shade veers off into bright cyan! I don't see HSL getting grey on the dark side.
This is fantastic, can't wait to incorporate it into my web design classes stuff.
Also, I do hope people begin to see the value of "designing toward intuition," I can't help but notice that efforts like these are exact opposite of what happened when (most of) the world forcibly converted to metric.
In the chromaticity diagram, is my Display-P3 screen mapping everything outside the triangle back into the triangle?
Yes, the diagram is a representation. Kind off like drawing 3D shapes on a 2D surface.
some nice OKLCH resources:
https://apps.apple.com/us/app/cone-color-picker-identifier/i...
https://sindresorhus.com/system-color-picker
https://evilmartians.com/opensource/oklch-color-picker
https://oklch.eerolehtinen.fi/
https://github.com/eero-lehtinen/oklch-color-picker
> It also works the other way around, where you can change the lightness value to create various color shades and there is no hue or saturation drift unlike in other color modes.
> In the example above, you can see that the OKLCH colors maintain consistent blueness across all of the shades, while in the HSL example, the lighter shades drift to purple and the darker ones muddy out towards grayish.
I see lots of automatic palette generator projects where the shades of each color are generated with OKLCH by only varying the lightness value on some chosen base color. The problem I find is if you look at popular open source palettes, the way the hand-crafted hue and saturation values vary across the shades for different hues isn't that predictable (the curve of the hue/saturation values over shades aren't straight lines or typical easing curves).
Hawking my own tool (using HSLuv with RGB for now), but you can load and compare the hue and saturation curves as they vary over shades of a color using example palettes from Tailwind 3, USWDS and IBM Carbon, plus tweak each shade to your liking:
https://www.inclusivecolors.com/?style_dictionary=eyJjb2xvci...
So I think OKLCH is a nice starting base for palettes and a quick way to generate a color you need in CSS, but I think designers will always need to tweak the hue and saturation of each shade so it looks just right as there's no single right answer you could encode into the color space.
Wow, this might be the best use of HSLuv so far, I'm going to add it to the examples page https://www.hsluv.org/examples/
Hi Alexei, thanks for your work on HSLuv! I love the simplicity of it, where you can use HSLuv as mostly a drop-in replacement for HSL which most designers are familiar with.
I keep seeing new tutorials on designing accessible palettes that still use HSL, where the WCAG2 contrast breaks and goes all over the place as you vary the hue and saturation. HSLuv makes life so much easier here and lets you focus on exploring colors that you know will pass, using a familiar looking color picker.
This. oklch requires you to be some sort of expert sage. HSLuv is so easy to grok.
Oklch is so cool, My website has a single hue colourscheme derived completely from the date so that every day is a new colour.
https://adithyanair.com
Thanks for this post. Hackernews is sometimes awesome for learning opportunities like this. Never heard of the model, thankful for the article.
How does oklch compare to CIELCh(uv)? I've been using that seemingly similar system to pick uniform colors.
Here's the original post explaining the color space. The ideas are very similar, OKLAB used a different white point
https://bottosson.github.io/posts/oklab/#what-about-existing...
Quote:
This is an aim, which I am not sure fully addressed. Think of the reason why can't I get oklch or any other method of color definition in HTML to produce the "gold color" as we humans think of it.The fundamental reason you can't get a truly convincing "gold" color using a single value in oklch, rgb, or any other color definition is because gold is a material, not a color.
What our brain perceives as "gold" is not a single, flat hue. It's a complex interplay of light, reflection, and texture.
Point is, even with sophisticated CSS involved with linear gradient it is still a challenge
See demo at https://jsfiddle.net/oyw9fjda/
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I was wondering about this exact subject the other day when working on some web dev task. Now I know why this way is better.
seems like a great idea, this will make working with colors so much easier
jesus fuck the whole discussion here is ptsd inducing... you need at least color accurate monitoring (including $25-30K calibrated monitor if you want to discuss rec2020-beyond) before judging if the output color looks "correct", and as correct here includes perceptually uniformity, then your monitor is crucial since light emitting technologies in the market are wildly varied.
this is _especially_ vital if you're not from color science & color correction industry, because that means you have no prior experience(s) with many problems & implications faced in the last 30 years of say, film post-production, which might have seen or solved some of these newly experienced "problems", which might've been caused by hardware choice(s) for example.
Awesome Post
HSV with extra steps?
These IP addresses being released at some point, and making their way into something else is probably the reason I never got to fully run my mailserver from my basement. These companies are just massively giving IP addresses a bad reputation, messing them up for any other use and then abandoning them. I wonder what this would look like when plotted: AI (and other toxic crawling) companies slowly consuming the IPv4 address space? Ideally we'd forced them into some corner of the IPv6 space I guess. I mean robots.txt seems not to be of any help here.
I think you commented on the wrong post :)
Oops,haha, you're right! Should have been https://news.ycombinator.com/item?id=45010183
Apologies! (I can't delete the post though, feel free to down-vote into oblivion)