Colourism

[Britney]

Prejudice or discrimination against individuals with a dark skin tone, typically among people of the same ethnic or racial group.

[Julian]

the [prejudice] or [discrimination] against individuals of a darker skin tone, like racism except it is usually among people of the same racial/[ethnic] group.

[Tracie Lynn]

dislike and unfair treatment of the members of a particular racial group who have a darker skin colour than others: