Why do you think human societies have given social meanings to differences in skin pigmentation (i. e., why do you think we separate people into "races" based on this factor) ?

People separate others into groups because it gets easier to them, and one of the main ones is by skin color. They automatically say white people are "rich" and black people are "criminals" while neither are totally true. Every person is their own person an can be anything they put their minds to.