As a black woman from New Orleans, I know that colorism is real. Because of how we've been treated, many people compare shades of brown. They treat women and men in accordance to their shade. When you are light skinned, they may call you "red," when they see you as a nickname. Also, in New Olreans, many people call you "black" as in "Say, black" when they see you if you are dark-skinned.
I think it comes for a subconscious recongiztion of the caste system established by white supremacy. I've had some of my friends say, "I'm black" but they say that I'm not. When this happens, I always try ro reassure them that the opinions of others cannot define us.