What I normally do is put all my color on the upper surfaces with patterns generally oriented span-wise. I'll typically use 3 or 4 colors with a "base" color of white (although there ultimately is very little white left). Conversely, the bottom is almost completely white with a small number of stripes oriented chord-wise in a single, different contrasting color.

This gives me three opportunities to determine plane orientation in the air:

1. Dominant color (colors on top, white on bottom)
2. Stripe orientation with respect to wing (span-wise on top, chord-wise on bottom)
3. Number of colors (large number on top, single color on bottom)

As an example, here's some pictures of my G-202 wing...the top: