add color-adjust function with example

Author: una

css-color-5/Overview.bs

@@ -36,9 +36,10 @@ Introduction {#intro}
 	and two colors with visually different lightness,
 	like yellow and blue, can have the same HSL lightness).
 
-	This module adds two functions:
+	This module adds three functions:
 	''color-mix'',
-	''color-contrast''.
+	''color-contrast'',
+	''color-adjust''
 
 	The perceptually uniform ``lch()`` colorspace
 	is used for mixing by default,
@@ -158,3 +159,35 @@ Selecting the most contrasting color: the ''color-contrast()'' function {#colorc
 
 	</div>
 
+Adjusting colors: the ''color-adjust'' function {#coloradjust}
+=====================================================
+
+	This function takes one <<color>> specification
+	and returns the result of adjusting that color,
+	in a given colorspace,
+	by a specified transform function.
+
+	Unless otherwise specified,
+	the adjustment is done in the ''lch()'' colorspace.
+
+	Multiple color functions can be specified.
+
+	<pre class='prod'>
+		<dfn>color-adjust()</dfn> = color-adjust( <<color>> [ <<color-function>> <<colorspace>>? ]?] )
+	</pre>
+
+	<div class="example">
+		This example produces the adjustment of red,
+		in ''lch()'' colorspace (the default),
+		with the lightness being increased by 30%.
+		The chroma and hue of red are left unchanged.
+
+		<pre class="lang-css">adjust-color(red, lightness(30%));</pre>
+
+		The calculation is as follows:
+		* sRGB red (#F00) is lch(54.2917 106.8390 40.8526)
+		* adjusted lightness is 54.2917 + 30 = 84.2917
+		* adjusted result is lch(84.2917 106.8390 40.8526)
+		* which is a gray color: rgb(218.5126% 218.5197% 218.4963%)
+	</div>
+