Re: buffer-face-set changes the fringe, is it a bug?

[Eli Zaretskii]

> Date: Tue, 7 Jul 2020 21:44:43 +0200 (CEST)
> From: Gregory Heytings via "Emacs development discussions." 
> <emacs-devel@gnu.org>
> 
> (2) When the 'default' face is remapped, Emacs completely ignores the 
> 'fringe' face, and uses the remapped 'default' face instead.

It doesn't "ignore", but because the remapped face specifies both
colors, the fringe colors don't show.  That's what happens when you
merge two faces one of which specifies both colors: if the face that
specifies both colors is merged last, the colors of the first one will
not show.