e) People even moving to other countries mostly breed within their own culture. A minority mix.
Why? Look at one of the recent Colonies, the USA.
Up until about 50 years ago, interracial/cultural unions have been taboo in the U.S. With that sanction falling away, we haven't seen most people mix out of race/culture, but a sizeable minority is (and if you include the removal of the old protestant/catholic division, a great many people are). Naturally blonde hair has already become extremely uncommon in North America. If even 10 per cent of people breed out of culture, it will only take a few generations for most people to be of mixed origin.