[css-color] Fix color() syntax to add srgb-linear, xyz-forms. Fix w3c#6858

Author: Chris Lilley

css-color-4/Overview.bs

@@ -3517,8 +3517,9 @@ Predefined Color Spaces</h2>
 		<dfn>color()</dfn> = color( <<colorspace-params>> [ / <<alpha-value>> ]? )
 		<dfn>colorspace-params</dfn> = [ <<predefined-rgb-params>> | <<xyz-params>>]
 		<dfn>predefined-rgb-params</dfn> = <<predefined-rgb>> [ <<number>> | <<percentage>> | none ]{3}
-		<dfn>predefined-rgb</dfn> = srgb | display-p3 | a98-rgb | prophoto-rgb | rec2020
-		<dfn>xyz-params</dfn> = xyz [ <<number>> | none ]{3}
+		<dfn>predefined-rgb</dfn> = srgb | srgb-linear | display-p3 | a98-rgb | prophoto-rgb | rec2020
+		<dfn>xyz-params</dfn> = <<xyz>> [ <<number>> | none ]{3}
+		<dfn>xyz</dfn> = xyz | xyz-d50 | xyz-d65
 	</pre>
 
 	<!-- check this test, remove any fallback testing -->

css-color-5/Overview.bs

@@ -1308,8 +1308,9 @@ The OKLCH chroma has dropped from 0.251 to 0.117.
 		<dfn>colorspace-params</dfn> = [<<custom-params>> | <<predefined-rgb-params>> | <<xyz-params>>]
 		<dfn>custom-params</dfn> = <<dashed-ident>> [ <<number>> | <<percentage>> | none ]#
 		<dfn>predefined-rgb-params</dfn> = <<predefined-rgb>> [ <<number>> | <<percentage>> | none ]{3}
-		<dfn>predefined-rgb</dfn> = srgb | display-p3 | a98-rgb | prophoto-rgb | rec2020
-		<dfn>xyz-params</dfn> = xyz [ <<number>> | none ]{3}
+		<dfn>predefined-rgb</dfn> = srgb | srgb-linear | display-p3 | a98-rgb | prophoto-rgb | rec2020
+		<dfn>xyz-params</dfn> = <<xyz>> [ <<number>> | none ]{3}
+		<dfn>xyz</dfn> = xyz | xyz-d50 | xyz-d65
 	</pre>
 
 	<!-- check this test, remove any fallback testing -->
@@ -1366,7 +1367,8 @@ the allowed [=channel keywords=] are:
 
 * <dfn value for="color()">x</dfn>, <dfn value for="color()">y</dfn>, <dfn value for="color()">z</dfn> are all <<number>>s
 	that correspond to the [=origin color's=] X, Y and Z channels
-	after its conversion to relative, D50-adapted CIE XYZ color space.
+	after its conversion to relative CIE XYZ color space
+	adapted to the relevant white point.
 
 	The parameters have the following form: