I'll tell you what I have found to be true.

Go dark on the bottom. It is really easy to see against the sky and you will be looking at that the most anyway.

Go with your bright/white on the top. Even on overcast days I can see the while on the top of the wing when I turning. Red turns to mud in the air unless the sun is shinning bright. I'm going to try bright yellow for my black and white bipe. I hear that hot pink is the best for overcast days. Not sure if I will do that to a Jungmann though.