In short, I’m trying to theme most of my install Adwaita Dark, but prefer Evolution to be themed Adwaita “light,” the default Adwaita. I’ve found plenty of how-to’s from a decade ago, but nothing very recent; one suggested added GTK_THEME=Adwaita to the .desktop file, but I can confirm that does nothing.
Thanks for the suggestion, but that does nothing for me… Even after a restart.
After sleeping on this, I decided to try again and found it works when env GTK_THEME=Adawaita:light is added to the exec line in the .desktop file at every instance; that is, the org.gnome.Evolution.desktop file has several exec lines and adding that string to everyone of them seems to do the trick.
An odd side-effect, however, is the body of the emails still briefly try to display in Adwaita Dark; strange.
Also, for this to persist any Evolution updates, I copied the .desktop file from /usr/share/applications to ~/.local/share/applications and edited it there. Could the “flicker” issue I reference above be related to that?