As noted by Luna, we can't use the house colours as they are used for other jobs.

The problem is that we don't know enough about the other schools/geographic placement, to be able to make a whole univsers.

Hogwarts/diagon-alley/hogsmeade/UK is what the 7 books are about. Yes, we do hear about Bauxbatons and Durmstrang, but not nearly enough to be able make an immersive universe.