bug#45799: 28.0.50; Faces shrink unreadable on GUI when foreground/background color set in TUI

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 12 Jan 2021 20:55:02 +0300
> From: Jean Louis <bugs@gnu.support>
> Cc: 45799@debbugs.gnu.org
> 
> > You didn't unset the colors, you've customized the default face.
> 
> Yes, I see.
> 
> But if default face on GUI 113 and on TUI 1, then user shall not get 1
> on TUI to customize also GUI to be 1. Can we agree on that?

This is not specific to TTY frames vs GUI frames.  You will have the
same problem if some frames use larger fonts for some reason: using
"M-x customize-face" will change the default face on _all_ of the
frames, and thus shrink the font size on the frames that used the
larger fonts.

Where does this end?

You are perceiving customize-face as a means for customizing the face
only on some frames, but that is not how that feature works, it
changes the faces globally, and for a good reason: Custom was invented
for users who want to avoid customizing Emacs in Lisp, so Custom
supports only simple use cases, and tries not to confuse the users by
providing too much flexibility and too much power.

If you want selective customizations, you must do that not via
customize-face.

> In my opinion if Emacs strategy on console is to display console's
> font's size then better affect only console even if there is no real
> effect, rather that then affecting the GUI and shrinking fonts to 1.

That's your opinion, and it's biased because you bumped into this
situation (quite unnecessarily, AFAIU).  the "usual" situations where
users invoke customize-face are very different.  What you intended to
do is not currently supported by customize-face, and I doubt that it
will ever be supported.

> With emacs -Q I cannot reproduce the theme settings. Problem is
> appearing when user has already set the foreground and background
> colors as then themes will not change those colors.

Then please try to come up with a simplest series of steps to
reproduce the problem with customize-themes.  There's some other
factor at work here, and we need to uncover it.