Actually, to get the color on the clear mate, All i use are Sharpie brand Markers!
Darker colors you may have to do a few passes because you'll miss some spots....and be sure to do it in good lighting so you don't miss areas.
Rainbow colors aren't difficult to get on, but Black is a bit more difficult and tends to remove itself when putting it on.......black takes a bit of time, but the colors apply nicely.
Hope that helps!