I came across the ( to me anyway as a VERY good question ) as to how come a lot of Light aircraft and indeed trials Military aircraft were painted white or grey respectively or whatever, making acquisition by the various cameras tricky at best?
The answer was that although there are thermal engineering issues for gliders and GCA, as far as mil' aircraft go no-one sees anything but a dark object in the sky, so it might as well be black.
I'm not sure how reassuring this would have been to people flying - one way or another - in the FRS/ FA2 testbed HS125 with Blue Vixen, which was painted mostly white and often had to formate on trials Sea Harriers in cloud !