bug#33799: 27.0.50; set-foreground-color completion shows background colors

[Glenn Morris]

Juri Linkov wrote:

> I don't know if readable background is needed for set-foreground-color
> like readable foreground is used for set-background-color.  I think
> your change to not use readable background is more correct because
> then the user will see how the selected color will fit with the background.
> This helps to select a suitable combination of foreground/background
> colors.  The same way maybe readable foreground should be removed
> from the completions of set-background-color.  This would allow to see
> how the current foreground color will look on different backgrounds
> in the completion list.

I think defined-colors-with-face-attributes probably needs yet another
argument, to control whether the non-varying component (be it foreground
or background) is a fixed value or a changing "readable" one.