bug#62994: [PATCH v3 0/1] Support styled underlines on tty Emacs frames

[Eli Zaretskii <eliz@gnu.org>]

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> From: Mohsin Kaleem <mohkale@kisara.moe>
> Date: Mon, 29 Jan 2024 08:06:38 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > The MSDOS frames are different from other TTY frames in that we can
> > know the default colors used by the MSDOS terminals.  That's why MSDOS
> > needs a special code there.  And yes, we want to keep this logic, for
> > MSDOS only.
> 
> Interesting. Didn't know MSDOS terminals expose that. Neat. Although why
> do we update the face spec (face->lface) itself in this case instead of
> only the foreground/background values which we do later anyways.

AFAIR, it's because those default colors are then used to define the
'default' face and the frame's fore/back-ground pixel values, so we
need the actual colors.

> face->lface seems to be the actual spec set in the theme/customisation
> display (unless I'm misunderstanding). If we change it wouldn't that
> alter what's shown in customize for example.

How can that alter what is shown, when the colors we stick in the face
are the exact colors that the screen uses?  It's like you take a
"blue" color that is specified by the special name "default" and
replace it with an actual "blue" -- how can the result be different.