"Black skin, white masks" is a book title that talks about how people with black skin sometimes feel like they have to act and think a certain way to fit in with people who have white skin. The author of the book, Frantz Fanon, talks about this feeling like you're wearing a mask - like you can't be your true self.
It's like when you're at school and all your friends like a certain game or TV show, but you don't really like it. You might pretend to like it too, so you can fit in with your friends. It's the same thing with how people with black skin sometimes feel like they have to act a certain way to fit in with people who have white skin.
But it's important to remember that everyone should be able to be themselves and not have to pretend or wear a mask, no matter what color their skin is.