Gentile observation for general culture. At this time and the current times. There were not contamination of white blood. That is due to the next reasons:
1) when some different genes are mixed is produced a genotype with more variability, that means less probability of genetic illness due to natural selection. 2) In the real life, the race doesn't exist in humans. If the race exist in humans the parents should be identical to their siblings.
3) Skin color can be changed by sunlight. If a human skin are exposed to UV rays enough time, mutates in order to protect it from skin cancer usually