Level 42--I had the same issue with my Galaxian marquee. I just used black latex paint (two coats) on the areas where they were spotted. I applied it from the backside of course. Looks great from the front. From the back of the marquee, you can tell it's been painted because it's not white anymore. This wouldn't work for the other colors of course, because they'd need to be somewhat transparent, but for the black, it worked great.