The squares next to foreground/background are placeholders for those controls I can't remember what they're called (colour wells?) where it shows the current colour, and clicking it brings up a colour picker allowing you to change. So separate ones for foreground/background rather than a radio button to say what you'll set and then a button to set it. Sorry for the confusion.

Any reason that you'd want to actually include a choice of ttk themes? Not sure that would really add anything positive to the overall UX (especially on Mac and Windows).

Worth discussing more about the name 'theme' (which seems to be common in other code editors) vs. 'text highlighting' vs. other alternatives.

Btw, is there a way to change the background colour and/or has that topic come up before?