Also due to other circumstances. There are Australian aboriginals who identify strongly with their spiritual ancestors and practice ancient belief systems, but who are as white as any European (due to their precursors being slaughtered in their thousands; some of the today's tribes feature
no 'full blood' Aboriginals.) White skin
most definitely does not always equate to Caucasian/European.
On some level it feels like by Star Trek's time there has been some serious intermingling anyway. It's part of the reason I never really had an issue with Picard being a Frenchman with an English accent. I always figured perhaps he simply reflects a mixed heritage?