There are many reasons for female labia nigra, but the main reason comes from heredity.
Some women are already dark when they are little girls. After investigation, her mother is also black, her grandmother is also black, and her aunts and aunts are all black.
Wearing tight underwear for a long time, excessive sexual life, leading to long-term congestion of labia, which in turn leads to pigmentation, but also causes labia blackening, but the degree is very limited, and genetic factors account for the vast majority.
The color of female labia varies greatly from person to person. Some people say that "a virgin's labia should be pink, if it is black, it means that she has too much sex …", which is totally nonsense. Those remarks are typical of sexual ignorance and are ignored.
Some medical institutions doing sexual health care have launched the "labial bleaching" project, but in fact, you don't have to care at all. Everyone's aesthetic standards are different. Why "unify" with others? There is absolutely no need to care. Make it black. Let it go. Genetic things cannot be changed, and they don't need to be changed. After sexual accomplishment, everyone will understand.