Most suppliers suggest masonry but as Mike said, oil-based paint bonds better to the poly. Murray McGregor (ITLD here) has painted thousands of boxes and had forty years to try various methods and came to the same conclusion.solvent based gloss paint, adheres better than masonry paint, seems more durable, and the paint seems to stay cleaner looking.
Love it! Although I'd like to do that myself, just the thought of doing it on only my two hives sounds too time consuming - perhaps I can paint a couple of fancy flowers at a time on them in situ later in the summer whenever I feel like it
Look wonderful - maybe you can resell them with a 50% mark up - I have no abilities in the artistic arena at all, if I lived anywhere near you I'd employ your talents.