If using the colour wheel to determine alignment, I wouldn't even bother using the DnD system. Instead I'd use the various descriptors in the colour wheel to define the basic personality. If you decide your high intelligence character focuses technology (a blue trait) but acts impulsively (a red trait) creating dangerous artifacts that run wild then you've got yourself a red/blue alignment and probably get on well in the Izzet guild. Since nothing interacts with alignment anyway, you probably don't even need to mention the colours, just look at them for inspiration for your basic PCs characteristics.