I would like to see humanity reach a point at which this would just be another difference, like whether or not the Doctor turned out to be ginger, or going from the very tall Colin Baker to the rather shorter Sylvester McCoy. Or having an accent that makes him sound like he’s from the north, or even further north than that in Scotland. Or appearing older or younger. I would like to see us reach a point at which the argument “the Doctor’s skin cannot be darker” sounds as ridiculous as “the Doctor cannot be played by a younger actor” or “the Doctor cannot be played by a Scottish actor” or any other objection of that sort.
The Doctor’s character is a Gallifreyan. Whatever he looks like, he is more different from any human being than humans with darker or lighter skin, and male and female humans, are from one another.
Perhaps reflecting on the Doctor’s alienness may help us get there?