Why are girls being laughed at for their dark skin?

When I was a sophomore, I met an African friend when I was learning English. She is from Senegal. Her name is Calva. Once I went out for dinner with Calva, Calva told me that she was often laughed at for her dark skin, so I comforted her. I said that in fact, in China's aesthetics, girls still regard white skin as beauty. There is an old saying in China that white covers all the ugliness, but you don't have to feel inferior for your dark skin.