Painting the blank white will keep the blank white but if the resin yellows when exposed to sunlight, you still end up with a yellowed board. As of late we’ve been expiriencing problems with the hot coats turning brownish yellow after a few hours out in the sun. This has bummed out our customers who have brought the boards back asking what gives?. If we sand into the glass job it appears that it is the hot coat is what is yellowing and not the lay-up underneath.