For colors, what you really want to look for is contrast. Generally you try to keep the top lighter than the bottom, and also include some directional cues, like diagonal lines, sunbursts, etc..

Using different colors, such as red/blue may look good on the ground, but up in the air they will look the same. I really like checkerboard on the bottom of wings and stabs. It gives great visibility that you are looking at the bottom rather than the top.

My Four Star is all red with just different decals on the top vs. the bottom, and orientation can be tough on a cloudy day, but there is nothing prettier than True Red Monokote in the sunshine. If I ever recover it, I'm going to checker the bottom.