“I would think interbreeding would hasten everyone to be more similar. That has not happened to a great degree.”
Says who? Black Americans are easily observed to be several shades lighter, generally, than black Africans. I’m sure if anyone bothered to do a scientific analysis, they could find other similar changes due to interbreeding.
I said "to a great degree". A slight change in skin color isn't much compared to what would have had to happen after Noah.