I'm sure you're right, a bunch of violence and other factors will have a big impact. I'm just saying that even under the assumption that multiracial relationships and babies will be the thing having an impact on phenotype diversity, it's not just averaging, even with skin color, which is where I think people get the idea that everyone will eventually just be brown. With American race rules and genetics in mind, black parents can have a very light-skinned kid and light-skinned parents can have a dark-skinned kid, and variations on this idea are the norm, not th exception, due to particulate inheritance and the various genes that dictate this having different impacts when their alleles pop up together in a new human.