My personal favorite is a shade called foxpeckerpink. It is quite a hit at social events. Bad guys laugh so hard when they see it that I don't ever have to shoot them. Saves ammo and jail time.
I find flat white works about as good as anything. If the light comes from behind, the white really shows up. If the light is in front of you, the sight will look black. No matter what colors you choose, the top of the sight must not blend with the target or you will get a bad sight picture and won't hit a thing.