One small change I made was I copied the "M.png" and called it "PG-13.png". That way a PG-13 film (which doesn't mean anything in Aus) gets rated M, which I guess is the closest / most conservative approximation.
Have you thought about making subtle grey transparent versions similar to original StreamedMP ones? This would be more in keeping with the theme of StreamedMP. Unfortunately I’m a total novice with GIMP.