The destruction of the human ego!
As long as groups of people look to distinguish themselves as being "better" than other groups race will be the easiest trait to point at.
Having said that if everyone were the same color then there would people who would say those with "green eyes" or "blue eyes" are smarter and better looking than those with brown or black eyes.
It's human nature for people to want to "compare" themselves to others and see how well they "stack up" against them.
Very few people would be happy if all schools changed from letter grades to a simple pass or fail. Equality equals mediocrity.
Ranking one another and looking for "differences" is our way of stating who is "best" based upon a criteria of a elitist majority.
Since there will not be a day where everyone is the same skin color racism will continue to be the easiest differentiator of them all.
Oddly enough sometimes the workplace allows an opportunity for some people of different races & cultures to befriend one another.