Define handling of COLR when CPAL is missing.

OFF_AMD2_WD.md

@@ -86,10 +86,10 @@ example, the placement of color stops in a gradient, or the alpha values applied
 to colors. The graphic capabilities supported in version 0 and in version 1 are
 described in more detail below.
 
-The COLR table is used in combination with the CPAL table (5.7.12): all color
-values are specified as entries in color palettes defined in the CPAL table. If
-the COLR table is present in a font but no CPAL table exists, then the COLR
-table is ignored.
+The COLR table can be used in two ways:
+
+1. If a CPAL table (5.7.12) is present the font is a color font whose color values are specified as entries in color palettes defined in the CPAL table.
+1. If no CPAL table is present the font is limited to the foreground color. This is ensured via by limitations on drawing capability defined in 5.7.11.1.8.3.
 
 **5.7.11.1 Graphic Compositions**
 
@@ -879,7 +879,7 @@ table would not require the corresponding graph of paint tables to be
 re-processed. As a result, using a PaintColrGlyph for re-used graphic components
 could provide performance benefits.
 
-**5.7.11.1.8 Glyph metrics and boundedness**
+**5.7.11.1.8 Glyph metrics, boundedness, and monochromatic use**
 
 **5.7.11.1.8.1 Metrics for color glyphs using version 0 formats**
 
@@ -923,6 +923,36 @@ details.
 Applications shall confirm that a color glyph definition is bounded, and shall
 not render a color glyph if the defining graph is not bounded.
 
+**5.7.11.1.8.3 COLR without CPAL**
+
+If a COLR table is present but there is no CPAL output is limited to
+varying the alpha value applied to the foreground color. The following additional limitations shall be imposed:
+
+COLR v0 and v1:
+
+1. The only valid palette index is 0xFFFF (the foreground color)
+
+COLR v1 only:
+
+1. The following composite modes are replaced by COMPOSITE_CLEAR if encountered
+   * COMPOSITE_SCREEN
+   * COMPOSITE_OVERLAY
+   * COMPOSITE_DARKEN
+   * COMPOSITE_LIGHTEN
+   * COMPOSITE_COLOR_DODGE
+   * COMPOSITE_COLOR_BURN
+   * COMPOSITE_HARD_LIGHT
+   * COMPOSITE_SOFT_LIGHT
+   * COMPOSITE_DIFFERENCE
+   * COMPOSITE_EXCLUSION
+   * COMPOSITE_MULTIPLY
+
+This ensures colors other than (foreground + alpha) are unreachable.
+
+NOTE: This is intended to make it possible for a rasterizer that supports
+rendering in the foreground color with antialiasing to support COLR without
+CPAL even if full color is not supported.
+
 **5.7.11.1.9 Color glyphs as a directed acyclic graph**
 
 When using version 1 formats, a color glyph is defined by a directed, acyclic