I'M A BEGINNING SIGNMAKER; I'm doing a BOX sign, 50"x30" with acrylic 3/8" plastic. I'll do the lettering on the inside, with a light cream color, the background will be medium blue. I planned to do the letters First, then roll out the Blue, (when the cream drys); WILL THE BLUE OVER THE CREAM BLOCK OUT THE LIGHT (from floresent tubes)? Or do the Blue over MASKING TAPE  letters, then remove the mask and paint theCream letters?