I have a plane that I have it covered in green on the bottom with two big stripes on both sides, and it is mostly white on the top of the wing. This allows me to distinguish it really well between top and bottom because one is dark and one is light. If I am looking at the light side, then that is the top. If it is dark, then it is the bottom. This really helps me when I am pretty far away and can't tell shapes or even certain colors very well. Up here in the pacific northwest, the clouds are here a lot and so a lot of stuff just kind of fades into the background.