bug#62237: 28.1 or higher: 24-bit true color breaks colours in Emacsen built without X under GNU Screen

[Eli Zaretskii]

> From: Sebastian Tennant <sdt@sebyte.me>
> Cc: 62237@debbugs.gnu.org
> Date: Fri, 17 Mar 2023 18:31:18 +0000
> 
> > No, Emacs 30 is good enough.  (Your report says Emacs 28.1, which is
> > why I asked.)
> 
> It's easy to miss the "or higher".

The "or higher" is not useful because it says nothing about the
versions you actually tested.  It could be Emacs 28.2, for example.
Please always tell all the details without assuming that our crystal
balls are clear enough to see them.

> > What is TERM set to on that system?
> 
> In a plain GNOME Terminal, i.e. outside screen:
> 
>  xterm-256color

That's 256 colors, not 64-bit true-color terminal, AFAIU.

> > It also says that your terminal actually supports only 88 colors.
> 
> How do you infer that?

By looking at the color names.

> > So you should unset COLORTERM in your environment
> 
> That's precisely the fix I discovered yesterday.

Then I guess this bug can be closed?

> According to:
> 
>  https://github.com/termstandard/colors
> 
> command:
> 
>  $ printf "\x1b[38;2;255;100;0mTRUECOLOR\x1b[0m\n"
> 
> shows your terminal is capable of truecolor if the word TRUECOLOR is
> printed in brown.  According to the result of this test, GNOME
> Terminal (3.38.3) _is_ truecolor enabled.

Which standard of true color does it support?

> I can observe the same broken colours in xterm (under the same
> conditions) shipped by Debian bullseye.
> 
> I'm sure it has to do with screen and will investigate whther or not
> my version of screen supports truecolor.

Thanks.