I experienced that problem, too! I later realized I had glued in the spar (that supports the wings and provides the dihedral) in reverse so that it now made an anhedral. By then, the wing roots and spar were solidly glued together and impossible to separate, so I had to clip off the spar ends, leaving just enough to glue the wing to, then glue the wings in place supported by blocks to obtain the right amount of dihedral. It complicated the build because the dihedral was never exact, and it left a wider than necessary gap. But it turned out not too bad! 
. I’ve seen museum examples painted metallic, or interior green. Other modeller’s work include weathered copper!