[css-color-4] Three-stage process for color function. Fix w3c#5046

Author: svgeesus

css-color-4/Overview.bs

@@ -3212,12 +3212,23 @@ Profiled, Device-dependent Colors</h2>
 	an [=out of  gamut=] color
 	<dfn export>can't be displayed</dfn>.
 
-	The ''color()'' function represents the color
-	specified by the first of its arguments that <dfn export>can be displayed</dfn>,
+	The first choice for the value of  the ''color()'' function
+	is that it represents the color
+	specified by the first of its arguments that
+	<dfn export>can be displayed</dfn>,
 	(that is, the first argument that isn't an [=invalid color=]
 	and isn't [=out of gamut=]).
+
 	If all of its arguments [=can't be displayed=]],
-	''color()'' represents <a>opaque black</a>.
+	second choice  for the value of the ''color()'' function
+	is that it represents the color
+	specified by the first of its arguments that represent
+	a [=valid color=], which will then be
+	<a>gamut-mapped</a> for display.
+
+	If all of its arguments are [=invalid color=]s,
+	the third choice for the value of the ''color()'' function
+	is that it represents <a>opaque black</a>.
 
 
 	<div class="example" id="ex-2020-oog-p3">