bug#47313: 27.1; highlight functions should accept colors too

[Eli Zaretskii]

> Date: Mon, 22 Mar 2021 09:29:24 +0000
> From:  scame via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> I wanted to use highlight-regexp to color some lines gray, but the command
> did not accept the color, it only accept faces, so I had to look for a 
> suitable
> face.
> 
> These highlight-* commands should accept color names too if the user
> wants a specific color, not a specific face,

Faces are not just colors, they have many additional attributes.

I'm not sure it is a good idea to make these commands accept both
faces and colors, as this could make the UI confusing and error prone.
It may be better to provide new commands, similar to the existing
ones, but which will accept only the colors instead of faces.

(You could of course define a face which specifies just the color, and
use that with highlight-* commands, but that is less user-friendly.)