[css-color-5] Clarify un-named components are still valid.

Author: svgeesus

css-color-5/Overview.bs

@@ -1495,6 +1495,11 @@ the allowed [=channel keywords=] are:
 		the excess <<number>>s at the end are ignored.
 		The color is still a [=valid color=].
 
+		For custom color spaces, if more <<number>>s or <<percentage>>s are provided than components listed in the optional components descriptor,
+		the additional values at the end are still valid,
+		but cannot be used in Relative Color Syntax.
+		The color is still a [=valid color=].
+
 		For custom color spaces, if fewer <<number>>s or <<percentage>>s are provided than parameters that the color space takes,
 		the missing parameters default to ''0''.
 		(This is particularly convenient for multichannel printers