Skin color can function very well as a class marker, like a uniform that can’t be taken off. Think of it as “low-tech” classism. The high tech version is, for example, the one conservatives project about:

Technologies of Race | American Identity and the War on Terror | 2021 Conversationalist Series - YouTube author of https://www.goodreads.com/book/show/6434826-toward-a-political-philosophy-of-race