Use the colour wheel as the basis for a single colourfull illuration that could be tessellated across the wrapping paper? color theory chart - beautifully simply way to learn this (plus the fact that I suck at combining colors LOL!
How to Use the Real Color Wheel (These are transparent primaries to paint with. Transparent yellow, transparent magenta and transparent cyan. These colors mixed will make red, blue and green, adding white will make them tints and opaque).