Although you don’t need to paint polystyrene hive parts, like the wooden equivalent, they will last much longer if you do.      Exterior masonry paints or even the Cuprinol shades can be used.   Painting the inside of the feeder is also recommended, especially if you are going to be using it for weak sugar syrup.     Make sure the finished surface in the feeder is roughened to aid the bees in climbing.   You can achieve this by adding sand to the paint on the 2nd coat.   The most difficult thing to do is deciding what colour you want to paint them?   blend them into the countryside with greens and browns, or go wild with pinks, yellow and purples!