Make use of the available light. Opaque colors all seem to turn black at altitude...I like to use an opaque on the fuse and fin, and transparent on the wings and stab. The light shining through the wings makes for better color recognition, and you can use a smallish piece of chrome on one wingtip that will catch light and flash, giving you an indication of upright/inverted by which side of the fuse it's on. Right now I'm experimenting with a black fuse and Fluorescent pink wing on a foamie sailplane...so far, so good.