Anyone who espoused that view openly, sure. That doesn't mean it wouldn't happen, in ways that weren't considered socially unacceptable. Looking 'more' black is already fairly widely 'treated' on an individual level by cosmetics and hair treatments, from what I've read, and that doesn't get much outcry. I've also read that 'more black-looking' black people have trouble finding mates, even among the black community. If that's accurate (and I have no idea, honestly) it could also be counted as another form of 'treatment', in a long term sense, by way of natural(?) selection.