bug#36304: 27.0.50; request: switch to the superior HTML #RGB convention for colors

[Eli Zaretskii]

> From: Pip Cet <pipcet@gmail.com>
> Date: Fri, 28 Jun 2019 09:28:53 +0000
> Cc: rms@gnu.org, 36304@debbugs.gnu.org
> 
> > > -    (cond ((and (>= len 4) ;; X-style "#XXYYZZ" color spec
> > > +    (cond ((and (>= len 4) ;; "#XXYYZZ" color spec
> >
> > Is #XXYYZZ no longer considered "X-style"?
> 
> I would say no, since X's interpretation of #f00 is a little different
> from the HTML/CSS/SVG interpretation.

Then maybe we want to refer to HTML/CSS/SVG?

> Complete updated patch attached.

LGTM, with one comment:

> +The returned value reflects the standard Emacs definition of
> +COLOR (see `Colors for Faces' in the Emacs manual), regardless of

Our convention is to say

  see the Info node `(emacs) Colors for Faces'

to refer to the Info manual.

Also, I think this change warrants an entry in NEWS.

Thanks.