I know about tinctures, furs, and metals, a friend directed me to a long article on heraldry in Polish. :)

Colors are tied to the patron deity of a house. I.e. War Queen's color is blood red, so her house uses red-and-black scheme; Noble Queen's color is gold and her house goes with gold-and-silver; Life-Giver's color is silver, and the house has silver-and-gold.
I gave the Dibeartach Lan silver-and-black to avoid black-and-brown, which would probably be too dark, and now I've got a problem when making a CoA for Bhais Lan, who are associated with death (black-and-silver?)

I don't have a deity associated with purple or blue. Technically, the Water Prince would count for blue, but the element deities are not powerful enough to warrant a house. Maybe I'll consider a house for all four element deities, and then the color scheme might be blue-and-something.

I've been thinking of making a house for the deity of magic, but the fact magic is supposed to be rare kept me from doing it.