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

On Friday, July 17th, 2026 at 11:21 PM, Eli Zaretskii <[email protected]> wrote:

> > Date: Fri, 17 Jul 2026 11:02:17 +0000
> > From: Heime <[email protected]>
> > Cc: [email protected], [email protected]
> >
> > On Friday, July 17th, 2026 at 6:08 PM, Eli Zaretskii <[email protected]> wro=
te:
> >
> > > > Date: Thu, 16 Jul 2026 20:50:36 +0000
> > > > From: Heime <[email protected]>
> > > > Cc: Eli Zaretskii <[email protected]>, [email protected]
> > > >
> > > > On Friday, July 17th, 2026 at 3:48 AM, packrat386 <[email protected]=
m> wrote:
> > > >
> > > > > "Heime" <[email protected]> writes:
> > > > >
> > > > > > On Thursday, July 16th, 2026 at 5:42 PM, Eli Zaretskii <eliz@gn=
u.org> wrote:
> > > > > >
> > > > > >> > Date: Thu, 16 Jul 2026 02:56:34 +0000
> > > > > >> > From: Heime <[email protected]>
> > > > > >> >
> > > > > >> >
> > > > > >> > How can I get list of colour names and hex numbers (list-col=
ors-display)
> > > > > >> > that I can then use in my code with a loop.
> > > > > >>
> > > > > >> The function defined-colors will return the list of names of s=
upported
> > > > > >> colors.  The function color-values will return the RGB triplet=
 for the
> > > > > >> given color.
> > > > > >
> > > > > > How does the computation for white give 65535 ?
> > > > > >
> > > > > > "white" 65535 65535 65535
> > > > >
> > > > > 65535 is 0xFFFF. So the RGB values are 16 bit integers and "white=
" means
> > > > > the max of all three.
> > > >
> > > > I do not understand this.  If 16-bit numbers require a 4-digit hex =
value
> > > > like FFFF, why does the hex values for white when calling (list-col=
or-display)
> > > > display #FFFFFF - which is only a 2-big hex value for each colour?
> > > > When I look for white using (list-color-display) I get a hex value =
of
> > > > #ffffff.  I do not understand this because if each colour is 16-bit
> > >
> > > There are different representations for the RGB specification of a
> > > color, you can have 3 or 6 or 9 or 12 hex digits.  See "Color Names"
> > > in the ELisp manual.  The relations between them are somewhat complex=
,
> > > and you don't need or want to dig into this in almost all cases.  Jus=
t
> > > use 16 bits per component and 12-digit specs all the time, and Emacs
> > > will do the rest.
> >
> > When I look at the definition of faces, I almost always see people
> > using #RRGGBB - 6 hex digits, 2 digits per colour.  That is 256
> > shades per colour.  Furthermore, although (color-values colour-name)
> > gives values in the range 0-65535 per colour, the hex value displayed
> > at the end in still #RRGGBB - meaning that the actual colour is lost.
>=20
> WHY DO YOU CARE???
>=20
> You ask questions and get the best answers we can provide.  Until and
> unless what these answers say doesn't actually work when you try, why
> do you insist on digging into the Emacs's sources that might do stuff
> differently, for whatever reasons?
>=20
> I could perhaps sit down and explain to you in a very detailed fashion
> why you see in faces.el what you see, but why should I invest that
> non-trivial effort?  And why should you insist on asking about that,
> when you evidently didn't even try what you were suggested to do?

An explanation would be good, but then I have to decide what to use in=20
practice, which undoubatedly is more important.
=20
> Understanding why we do in Emacs's sources what we do there requires a
> lot of knowledge about the internal workings and the history of Emacs.
> All of that is completely irrelevant to writing code on the level on
> which you are now.  So please take the advice you are given and try
> it, and only ask followup questions about "other ways of doing that"
> if the advice doesn't work for some reason.
>=20
> Okay?

What is the advice exactly?  I am writing colour faces and want to compute
contrast ratio to support accessibility rules.  It makes a difference what=
=20
hex values I use.  You suggest using names, many people use  #RRGGBB.
There does not seem to be any clear agreed way. =20

If I take a name, the colour values for the name are in range 0-65535
which requires #RRRRGGGGBBBB.  And the hex value displayed is #RRGGBB.
Which value should one use, the common #RRGGBB or the #RRRRGGGGBBBB.

For instance modus-themes uses #RRGGBB.

Emacs internally uses 16-bit per component, but the displayed hex code
is usually 6-digit.  Can't people see a problem with this! =20

The common, practical hex format in Emacs and web standards is #RRGGBB.
Seems to me that developers are routinely disregarding any improvements
with higher bit colours.  But internally you care about them and use them.