What are OKLCH colors?
78 comments
·August 25, 2025chrismorgan
jakubkrehel
This is super insightful, thank you! I wrote the article and will make changes to explain this better :)
Diggsey
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...
cubefox
> The red in that gradient is way darker than the rest of it.
It doesn't look significantly darker to me.
Vingdoloras
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).
chrismorgan
Sorry, fixed.
djoldman
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?
layer8
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.
ta8645
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?
chrismorgan
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.)
ta8645
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?
shrx
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).
layer8
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.
adornKey
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).
twhb
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.
masklinn
> 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.
background-color: rgb(from var(--base-color) calc(r - 76.5) g calc(b + 76.5));fidotron
> 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.
rafram
There’s no green shift at all in that example on my display. Could your calibration be off?
fidotron
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.
JimDabell
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:
Discussed on Hacker News here:
https://news.ycombinator.com/item?id=43073819 (6 months ago, 30 comments)
vanderZwan
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.
hackrmn
> 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).
necovek
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).
Geenkaas
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...)
JohnKemeny
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.
pavlov
He’s Swedish, so I bet OK is actually short for “Ottossons kulör” but he’s just being modest.
Aissen
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).
chrismorgan
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).
ksec
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.
adrian_b
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.
rollcat
Wherever you're working with colors and text/emblems, please also consider contrast and legibility: <https://apcacontrast.com/>
robin_reala
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.
ximm
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.
robin_reala
Oh, interesting, I’d missed that. Good info, thanks!
seanwilson
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.
robin_reala
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.
once_inc
My mind immediately translated OKLCH into "Oklachroma".
Daub
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.
DeusExMachina
My understanding is that it's the same with higher resolution.
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.