[css-color-5] more explanatory prose

Author: svgeesus

css-color-5/Overview.bs

@@ -29,13 +29,24 @@ Introduction {#intro}
 	Currently Sass, calc() on HSL values, or PostCSS is used to do this.
 	Preprocessors are unable to work on dynamically adjusted colors,
 	and all current solutions are restricted to the sRGB gamut
-	and to the perceptual limitations of HSL.
+	and to the perceptual limitations of HSL
+	(colors are bunched up in the color wheel,
+	and two colors with visually different lightness,
+	like yellow and blue,
+	can have the same HSL lightness).
 
 	This module adds three functions:
 	''color-mix'',
 	''color-contrast''
 	and a way to modify existing colors.
 
+	The perceptually uniform ``lch()`` colorspace
+	is used for mixing by default,
+	as this has no gamut restrictions
+	and colors are evenly distributed.
+	However, other colorspaces can be specified,
+	including ``hsl()`` or ``srgb`` if desired.
+
 	Issue(3187): there are two proposals for color modification.
 	The CSS WG expects that the best aspects of each
 	will be chosen to produce a single eventual solution.