lab()

• Functional notation: lab(L a b [/ A])
  • L is a <number> between 0 and 100 or a <percentage> between 0% and 100% that specifies the CIE Lightness where the number 0 corresponds to 0% (black) and the number 100 corresponds to 100% (white).
  • a is a <number> between -125 and 125 or a <percentage> between -100% and 100%, specifying the distance along the a axis in the Lab colorspace, that is how green/red the color is.
  • b is a <number> between -125 and 125 or a <percentage> between -100% and 100%, specifying the distance along the b axis in the Lab colorspace, that is how blue/yellow the color is.
  • A (alpha) can be a <number> between 0 and 1, or a <percentage>, where the number 1 corresponds to 100% (full opacity).

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

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

The following example shows the effect of varying the lightness, a-axis, and b-axis values of the lab() function.

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

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

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

div {
  width: 50px;
  height: 50px;
  padding: 5px;
  margin: 5px;
  display: inline-block;
  border: 1px solid black;
}

[data-color="red"] {
  background-color: lab(100 125 125);
}
[data-color="red-a"] {
  background-color: lab(100 110 125);
}

[data-color="green"] {
  background-color: lab(75% -120 125);
}
[data-color="green-b"] {
  background-color: lab(75% -120 10);
}

[data-color="blue"] {
  background-color: lab(0 -120 -120);
}
[data-color="blue-light"] {
  background-color: lab(70 -120 -120);
}

The following example shows the effect of varying the A (alpha) value of the lab() functional notation. 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>

div {
  width: 50px;
  height: 50px;
  padding: 5px;
  margin: 5px;
  display: inline-block;
  border: 1px solid black;
}
#background-div {
  background-color: lightblue;
  width: 150px;
  height: 40px;
}

[data-color="red"] {
  background-color: lab(100 125 125);
}
[data-color="red-alpha"] {
  background-color: lab(100 125 125 / 0.4);
}

• The <color> data type for a list of all color notations
• LCH colors in CSS: what, why, and how?
• Safari Technology Preview 122 release notes: includes lab() and lch() colors.