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!
7 Paint Routines You’ll Never Regret Teaching (The Art of Education)
Here you can see the division of warm and cool colours. Warm colours are the more "bright" colours and cool colours are the more "dark" colours. Warm starts at oink and ends at yellow,cool starts at green and ends at purple.