bug#46493: [feature/pgtk] Low contrast region face

[Po Lu]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> Testing this on my laptop, I get the same colour in pgtk and not -- a
> very dark grey.  And that's because I use a dark theme in Gnome Shell,
> presumably?

I guess so, yes.  Though the GNOME Shell theme is separate from the GTK
stylesheet itself, as GNOME Shell uses a different toolkit.

> However, we ignore the theme for everything else, so "emacs -Q" gives me
> an Emacs with a white background -- and a very dark region face.

That shouldn't be problematic, right? Because we have the distant
foreground set to the GTK region foreground color, so there will always
be sufficient contrast.

> It's nonsensical to heed Gtk's settings for the region face when we
> don't heed it for the default background colour, so again I'm back to
> the same point: We should probably just remove that code and use the
> normal Emacs-determined face colours on (p)gtk, too.

I don't think so: it seems unduly harsh, since we also do the same on
other platforms such as Mac OS.

Users using a non-default GTK stylesheet should know of the
consequences, and can simply customize the region face to use a
different background color.