bug#50141: Current part of emacs red, other parts blue

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: jidanni@jidanni.org,  50141@debbugs.gnu.org
> Date: Sat, 21 Aug 2021 15:28:25 +0200
> 
> > Basically, faces were never designed to be window-specific.  Even
> > making them buffer-specific (via face-remapping-alist) is somewhat
> > tricky.
> 
> Yeah, I suspect we can't use faces here, but might have to add some new
> window-specific background colour setting?

What could that color setting be, except some face attribute?