A good rule for visibility is light color on top (white, yellow, cream), dark colors underneath (black, maroon, dark blue) with some contrasting color on both top & bottom. Contrast color should be close to square proportions for maximum visibility, and a good place to put them is on the wingtips or a stripe on the wing roughly the width of the wing chord.

Checkerboard patterns are popular for the underwing, but the problem is that 1" squares of black & white fade into gray at even a moderate distance, and gray against a gray sky is not a good formula.

A good place to divide the fuselage top & bottom colors is along the thrust line, to emphasize level flight or landing flare or whatever, and something to sight aileron & elevator deflection against when adjusting linkage.