The Importance of Banners

Colors of banners might be based on the wealth of a house in the first place. Certain colors come from certain plants, and if you have those plants in your country then those colors are cheaper. Or the harvest in conqueror the places with those plants. Purple dye comes from sea snails, which George Tyroshy expanded on that whole idea. The Witcher story eternal flame has a funny part about dye and how one house overthrows another because they're just too rich.