Well, supremacy isn’t necessarily a negative quality. Some white pepole are very content thinking of themselves that way. I’d say it’s more harmful for black people to learn to think of themselves as inherently subjugated.
And it’s not even close to fair to say that blackness is always given positive qualities either. In fact, the whole issue is that for centuries, “blackness” has been associated with being subhuman and stupid and worthless.
But yes, the fundamental problem is that it assigns qualities and values on the basis of somebody’s skin colour is a mistake. And specifically, the same mistake that has seen so much injustice done to black people. We need to free ourselves from that thinking.