[css-color-5] separate section for colorspaces

Author: svgeesus

css-color-5/Overview.bs

@@ -74,6 +74,29 @@ Introduction {#intro}
 	However, other colorspaces can be specified,
 	including ``hsl()`` or ``srgb`` if desired.
 
+Colorspaces {#colorspaces-section}
+==============
+
+Mixing or otherwise combining colors
+has different results depending on the colorspace used.
+In some cases, the result of physically mixing two colored lights is desired
+(in that case, the CIE XYZ colorspace is appropriate, because it is linear in light intensity).
+In other cases, colors which are evenly spaced perceptually are desired
+(in which case, the CIE Lab colorspace is designed to be perceptually uniform).
+Alternatively, maximising chroma so that color mixtures follow along the hue wheel is wanted
+(CIE LCH works well for this).
+Lastly, compatibility with legacy Web content may be the most important consideration.
+(the sRGB colorspace, which is neither linear-light nor perceptually uniform, is the choice here).
+
+
+<pre class='prod'>
+	<dfn>&lt;colorspace></dfn> = srgb | hsl | hwb | xyz | lab | lch
+</pre>
+
+When no [=colorspace=] is specified,
+the mixing is done in the ''lch'' colorspace.
+The [=xyz=] colorspace is CIE XYZ, with a D50 whitepoint, and allows computation to be done
+in a linear-light-intensity space.
 
 
 Mixing colors: the ''color-mix()'' function {#color-mix}
@@ -95,9 +118,6 @@ Mixing colors: the ''color-mix()'' function {#color-mix}
 	<dfn>&lt;mix-component></dfn> = <<color>> [ <<percentage>> | <<color-adjuster>>+ ]?
 </pre>
 
-<pre class='prod'>
-	<dfn>&lt;colorspace></dfn> = srgb | hsl | hwb | xyz | lab | lch
-</pre>
 
 <pre class='prod'>
 	<dfn>&lt;color-adjuster></dfn> = [ [
@@ -113,11 +133,6 @@ Mixing colors: the ''color-mix()'' function {#color-mix}
 	<dfn>&lt;hue-adjuster></dfn> = hue [shorter | longer | increasing | decreasing | specified ]?
 </pre>
 
-When no [=colorspace=] is specified,
-the mixing is done in the ''lch'' colorspace.
-The [=xyz=] colorspace is CIE XYZ, with a D50 whitepoint, and allows computation to be done
-in a linear-light-intensity space.
-
 Arguments are normalized as follows:
 
 1. When a percentage is specified without any [=color-adjuster=]s,