There are a few threads on this already, if you do a search, you can probibly find lots of info.

That said, you usually want big blocks of contrasting colors. Lettering, checkers and such usually are too small to be seen. I generally plan on stripes or blocks no smaller than 4" wide, but even that is a bit small at times. No one color by itself is the answer, it's the combination of 2 or more.

Black/yellow is popular. International orange with a dark blue or green works, I've seen a couple of planes with that. Orange and white or red and white aren't bad either.