the easiest way it so spray the letters and the color you want let it dry, then put a few layers of chapstick over the letters, then spray the whole thing the other color that you want and once that is dry you should be able to wipe that layer off because of the chapstick, leaving the 1st color you sprayed
what i did was paint the eintire thing and sanded off the lettering so it was nice n shiney, but i think the chap stick thing mightve been easier. but mine turned out great!