I just noticed this, in Properties Affected by Forced Colors Mode

If the color value indicates a “fallback” color (as in the color() function in [CSS-COLOR-5]) and that fallback color is a system color, then the color is forced to that system color.

Concerns over the value and added complexity of a (potentially long) fallback color list for color() were raised: #5931 #5904 and similarly for device-cmyk() #6721 which resulted in their being dropped from CSS Color 4.

So, I guess simply drop the quoted bullet item?