“A slight change in skin color isn’t much compared to what would have had to happen after Noah.”
Yes, but that’s only a superficial observation. I don’t think anyone has done any rigorous study on this, so we can’t quantify the effects of interbreeding. Without that, we can’t know how much of any changes we do observe are due to interbreeding, or might be due to environmental adaptation.
In other words, it’s a badly compromised example, since you can’t control for other experimental variables.
A very unconvincing example. I can easily recognize people descended from non-European ancestors that have been here 400 years.