Upper case is used for Black when referring to Black people because, in that context, Black refers to a culture rather than a color. Similarly, we capitalize words like Native, Hispanic, as well as national descriptors eg French, English, American, etc.

Capitalizing White is a bit more complicated. One may argue that White is a culture also, and capitalize it said way. I see some Black writers capitalize white when referring to white people, probably for that reason. I see the writer of this article capitalizes White -- Ms. Gaines, if you read this, could you comment please? It's worthwhile to note that whiteness is a culture, just one culture among the thousands of cultures in the world, and not the universal human norm. I used to capitalize white for that reason.

Only problem is, many white supremacists capitalize white, so as to exalt themselves over others. They ruined it for the rest of us; other writers of Euro descent who capitalize white risk being mistaken for a white supremacist. That's why I no longer capitalize white.