Back in the slave days, white people were slaving black people because of their dark skin.
Today, most of the time being black and having black skin is considered ugly and hated upon.
There's black people who have brown skin who are not really the color 'black'. And because of the way black people's skins are looked down upon.
It's okay to call white people white people because white people were not slaved for their pale skins, beaten and raped because of their pale skin. Being considered 'white' is highly looked upon in society as 'acceptable' and 'not different'.
So if you don't understand this, to make this short and sweet. White people were not treated the way that black people were treated in the slave days, being segregated based on their skin, and being treated unfairly.
I think that you have no idea what black people went through in the earlier days, and if you truly do not care to read what happened them, how they were treated and how they overcame everything, than you don't need to asks question.