On Wed, Jul 19 2023, Eli Zaretskii wrote:

> That's exactly what I meant: when you customize the foreground color
> of a face, show the candidates as text in that color on the background
> of the face's background color, and when you customize the background
> of a face, show the candidates as background with the text in the
> foreground color of the face.  IOW, show the face with its both colors
> as it will look if this candidate is chosen.

OK. Here is a patch that should do this: