evansb, you beat me to it. Many gliders were anything but white in the pre-composite days. Some aerobatic gliders still are, though that obviously has more to do with visibility issues. Quite a few natural metal-coloured ones around too, witness the Blanik, or the I.S.
Now, why do most bizjets have boring, dopey-looking stripes down the side? My personal jet will be black, with hot-rod style FLAMES down the sides!
(Note the 'will', ain't giving up on the dream, nuh-uh!)