I've painted probably 100 VHF and UHF antennas and have never seen a problem. I've even tested Ku and Ka band satellite feed radomes with various spray paints and some have very little effect with just one coat. Others attenuate a lot, but painting a plastic radome is a little different than painting a metal antenna.
One thing that does happen is a coating of paint or anything on a metal antenna will cause it to resonate slightly lower in frequency because you are going from a bare metal radiator to one that has a dialectic coating. Its the same effect when going from a bare wire antenna for HF compared to using insulated wire and the effects from that can be several inch differences in wire lengths.
I'm not sure if you will notice on a small Yagi but on long lengths of wire its very noticeable.
Last edited by prcguy; 02-17-2017 at 11:08 AM..