• Functional notation: oklch(L C H [/ A])
  • L is a <number> between 0 and 1 or a <percentage> between 0% and 100%, where the number 0 corresponds to 0% (black) and the number 1 corresponds to 100% (white). L specifies the perceived lightness.
  • C is a <number> or a <percentage>, where 0% is 0 and 100% is the number 0.4. It is a measure of the chroma (roughly representing the "amount of color"). Its minimum useful value is 0, while the maximum is theoretically unbounded (but in practice does not exceed 0.5).
  • H is a <number> or a <angle> that specifies the hue angle along the positive "a" axis (toward purplish red), 90deg points along the positive "b" axis (toward mustard yellow), 180deg points along the negative "a" axis (toward greenish cyan), and 270deg points along the negative "b" axis (toward sky blue).
  • A (alpha) can be a <number> between 0 and 1 or a <percentage> between 0% and 100%, where the number 1 corresponds to 100% (full opacity).

<oklch()> = 
  oklch( [ <percentage> | <number> | none ] [ <percentage> | <number> | none ] [ <hue> | none ] [ / [ <alpha-value> | none ] ]? )  

<hue> = 
  <number>  |
  <angle>   

<alpha-value> = 
  <number>      |
  <percentage>  

The following example shows the effect of varying the L (lightness), C (chroma), and H (hue) values of the oklch() color function.

<div data-color="blue"></div>
<div data-color="blue-light"></div>

<div data-color="red"></div>
<div data-color="red-chroma"></div>

<div data-color="green"></div>
<div data-color="green-hue"></div>

[data-color="blue"] {
  background-color: oklch(60% 0.4 240);
}
[data-color="blue-light"] {
  background-color: oklch(90% 0.4 240);
}

[data-color="red"] {
  background-color: oklch(100% 0.4 30);
}
[data-color="red-chroma"] {
  background-color: oklch(100% 0.3 40);
}

[data-color="green"] {
  background-color: oklch(60% 0.57 161);
}
[data-color="green-hue"] {
  background-color: oklch(60% 0.57 181);
}

The following example shows the effect of varying the A (alpha) value of the oklch() color function. The red and red-alpha elements overlap the #background-div element to demonstrate the effect of opacity. Giving A a value of 0.4 makes the color 40% opaque.

<div id="background-div">
  <div data-color="red"></div>
  <div data-color="red-alpha"></div>
</div>

[data-color="red"] {
  background-color: oklch(50% 130 20);
}
[data-color="red-alpha"] {
  background-color: oklch(50% 130 20 / 0.4);
}

• The <color> data type for a list of all color notations
• A perceptual color space for image processing
• OKLCH in CSS
• Safari Technology Preview 137 release notes: includes oklch() and oklab() colors