I tracked down the bug reports and fix for the ugly GTK3 rendering

[dreamer]

I wondered why this hasn't been mentioned more, because it's "in your face" especially if you switch to a fully GTK3 environment like MATE. Maybe some drivers aren't affected. I thought it was limited to AMD, but it seems more drivers are affected. Maybe if you are using an SSD or a dark theme it's less of a "in your face" problem. It ruined GTK3 for me and made it look amateurish.

First bug report from April 2015.

https://bugzilla.gnome.org/show_bug.cgi?id=748498

Basically what comment 1 describes in the above bug report:
"Starting from gtk 3.18 on Xfce, this behavior is more evident than previous gtk versions. With or without a compositor, the black background is shown and is very ugly, especially on light themes. On gtk 3.16 I can use a compositor to solve the problem, but on 3.18 not."

One user fixed it by undoing an old commit to gtk (comment 22):
re-adding what was removed in https://gitlab.gnome.org/GNOME/gtk/comm ... e126700afe fixes this on my system

More bug reports:
https://gitlab.gnome.org/GNOME/gtk/issues/550
https://bugzilla.redhat.com/show_bug.cgi?id=1370791
https://bugzilla.gnome.org/show_bug.cgi?id=771708

Anyway, it was fixed 10 months ago in upstream GTK.
x11: Set a transparent background on windows by default - This avoids black flicker on compositing WMs when a window is first shown:
https://gitlab.gnome.org/GNOME/gtk/comm ... 69497478b0

Can this fix be back-ported to the test repo?

It seems gtk devs caused this by choosing black instead of transparent or main gtk window color (gtk2 does this).