After each fresh install of Artix Linux XFCE OpenRC I see this (but don't blame Artix, because I had this phenomenon in other distributions):
When choosing the Adwaita theme, I notice that the visual themes are mixed.
The background of Dolphin, Gimp, or some configuration windows is black...
I found an unscientific method to fix it (it has been working for over a year):
Reinstall all the packages present.
sudo pacman -S $(pacman -Qnq)
After this "cure", all the colors are correct everywhere ... on condition of commenting (add # at the beginning of the line) in /etc/environment the two lines:
# QT_QPA_PLATFORMTHEME=gtk2
# QT_STYLE_OVERRIDE=gtk
My two cents :)
All this mess was caused by a missing closing quote (https://forum.artixlinux.org/index.php/topic,2605.msg17179.html), a simple update should fix it.