Why’s skin colour such a massive thing?

Since ancient times fair skin has been viewed as desirable so there are even beauty products that lighten the skin. My mother has to order her skin products online or before then buy them on the military base b/c she is black and has no desire to be lighter but we live in Korea where fair skin is extremely important. People are wearing long sleeves and pants even in the summer to keep themselves pale. I can't count the number of times my mother got accused of stealing her own mixed race children b/c having non black father we are very light brown or yellow skinned. I remember that I used to want to be brown or black like Mommy but my father and paternal family was always like "Why you want to be dark and ugly?!" Message loud and clear. Fair skin is beautiful, dark skin is hideous.