Kenneth and Mamie Clark were a husband and wife team who did research on how kids feel about differences in skin color.
They showed kids pictures of black and white dolls and asked them which doll they liked better. A lot of the kids said they liked the white doll better, even if they were black themselves.
Kenneth and Mamie thought this was because of something called segregation. That means people were separated by skin color and black people weren't treated as nicely as white people. So the kids learned to like white things more.
They told lots of people about what they found and it helped make things a little bit better. People started to see that it wasn't fair that some kids thought white was better than black. And they tried to change it so everyone was treated the same no matter what color their skin was.