A Theme can change the colors of the Editor. So this will apply to a Theme.
You can still change the colors in the Appearance Options.
I recently updated a Solarized Dark theme with better selection colors.
Here it is… Solarized Dark theme broken on Windows - #7 by AntoniDol
I’ve create some FAQ-posts in \rScrivenerThemeBuilder
If you’re patient, I’m writing a book about Mastering Scrivener Themes…