Re: Retrieving color names and hex values using list-colors-display for coding purposes

On Saturday, July 18th, 2026 at 3:38 AM, Eli Zaretskii <[email protected]> wrote=
:

> > Date: Fri, 17 Jul 2026 14:55:28 +0000
> > From: Heime <[email protected]>
> > Cc: [email protected], [email protected], [email protected]
> >
> >
> >
> >
> >
> > Sent with Proton Mail secure email.
> >
> > On Saturday, July 18th, 2026 at 2:34 AM, Eli Zaretskii <[email protected]> w=
rote:
> >
> > > > Date: Fri, 17 Jul 2026 14:28:11 +0000
> > > > From: Heime <[email protected]>
> > > > Cc: uzibalqa <[email protected]>, [email protected], help-gnu-emac=
[email protected]
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > Sent with Proton Mail secure email.
> > > >
> > > > On Saturday, July 18th, 2026 at 1:33 AM, Eli Zaretskii <[email protected]=
g> wrote:
> > > >
> > > > > > Date: Fri, 17 Jul 2026 13:22:13 +0000
> > > > > > From: uzibalqa <[email protected]>
> > > > > > Cc: Heime <[email protected]>, [email protected], help=
[email protected]
> > > > > >
> > > > > > If the advice is always to use #RRRRGGGGBBBB, which is also alw=
ays the advice
> > > > > > for my cases,  then how (list-colors-display) showing me #RRGGB=
B follows the
> > > > > > advice you described?  To follow your advice, display #RRRRGGGG=
BBBB, not
> > > > > > the currently displayed #RRGGBB.
> > > > >
> > > > > Are you writing list-colors-display?  If not, why is it important=
 that
> > > > > it shows 6-digit RGB values?
> > > >
> > > > Because colour-values on the name are in range 0-65535, a range tha=
t
> > > > definitly requires hex RRRR and not hex RR.  The hex value is uniqu=
e,
> > > > consequently using  RR instead of RRRR is incorrect.
> > > >
> > > > Multiple (0-65535) values map to the same #RR value, breaking uniqu=
eness
> > > > and accuracy.  Colour accuracy matters for contrast calculations, a=
ccessibility,
> > > > and precise colour matching.  The emphasis on the importance of 6-d=
igit
> > > > hex values is that they uniquely and accurately represent the colou=
r in
> > > > the standard hex format.
> > >
> > > All of the above are reasons to use 16-bit values for each RGB
> > > component.  That way, you don't lose accuracy when specifying a color=
.
> >
> >
> > list-colors-display is an interactive function in facemenu.el, which is
> > part of GNU Emacs.  It should look at the range of values and determine
> > whether #RRRRGGGGBBBB should be used as display.
>=20
> Not necessarily.  It works with a list of 256 colors, so the full list
> available on the platform is not relevant.

I can take the RGB values, for instance 60000, get 60000/65536, which is
0.915, and reduce to 256 colours via 0.915*256 to get 234.
Such a mapping from 16-bit values to 8-bit values should be ok.

Looks to me that I can take #RRRRGGGGBBBB and obtain a close #RRGGBB.
Basically, the same colour name gives slightly different colour depending
on the terminal supported colours, whether 256 or 16, etc.   The same colou=
r
name does not render exactly the same on different torminal systems.

> Once again, please don't look at that command as guidance for which
> RGB specifications to use in your programs.

But I can use the colour names?  I could then make my own hex conversions
and compute contrast values.  Could I rely on the colour names from=20
(defined-colors).  The names should be identical to the ones from=20
list-colors-display, right?