[css-fonts-4] Color palettes have to always be complete

Author: litherum

css-fonts-4/Overview.bs

@@ -6348,6 +6348,10 @@ User-defined font color palettes: The ''@font-palette-values'' rule</h3>
     In addition, it allows overriding a set of colors from a palette in the font
     with colors described by the web author.
 
+    A palette is always <i>complete</i>, meaning that it is impossible to describe
+    a palette which has missing colors. If colors would be missing, they are taken
+    from the palette within the font identified by the 'base-palette' descriptor.
+
     The ''@font-palette-values'' rule consists of the ''@font-palette-values'' at-keyword
     followed by a block of descriptor declarations.
     It has the following syntax:
@@ -6540,7 +6544,7 @@ Specifying the base palette: the 'base-palette' descriptor</h4>
     If a font does not contain any color palettes,
     no colors are included in the initial color palette
     represented by this ''@font-palette-values'' rule.
-    Colors can be added to the color palette
+    Colors in the palette can be overridden
     by using the 'override-color!!descriptor' descriptor in the ''@font-palette-values'' rule.
 
     Strings specified in the value of this descriptor
@@ -6557,7 +6561,7 @@ Overriding a colors from a palette: The 'override-colors!!descriptor' descriptor
     Initial: N/A
     </pre>
 
-    This descriptor overrides or adds colors
+    This descriptor overrides colors
     to the initial color palette represented by this ''@font-palette-values'' rule.
 
     The '@font-palette-values/override-colors' descriptor takes
@@ -6566,11 +6570,8 @@ Overriding a colors from a palette: The 'override-colors!!descriptor' descriptor
     an entry into the palette an a color to replace it with.
 
     For each key/value pair in the value of this descriptor,
-    if the initial color palette represented by the ''@font-palette-values'' rule
-    (i.e. by using the 'base-palette' descriptor)
-    already includes a color at the index of the key,
-    that color is overwritten by the color specified in this descriptor's value.
-    Otherwise, a new color is added to this color palette at the index of the key.
+    the color with that key in the initial palette (i.e. by using the 'base-palette' descriptor)
+    is overwritten by the color specified in this descriptor's value.
 
     Palette index entries
     in the ''@font-palette-values/override-colors'' descriptor