Racial divisions is something that the US has struggled to overcome for long periods of its history, finally starting to gain equality for all after a series of US Supreme Court judgments in the 1950's and 60's which were implemented by the Federal Government (sometimes over the opposition of various state level governments).
However, the area of racial tolerance and discrimination between people based on their race is something that is just below the surface, and can sometimes come to the forefront fairly quickly (and has the ability to shock people when that happens). Consider this case where shoppers inside a Walmart store heard an announcement for all black shoppers to leave (link to article):
A Walmart store announcement ordering black people to leave brought chagrin and apologies Wednesday from leaders of the company. A male voice came over the public-address system Sunday evening at a store in Washington Township, in southern New Jersey, and announced: "Attention, Walmart customers: All black people, leave the store now."Obviously, this was something that the management of Walmart would never have accepted.
Shoppers in the store said a manager quickly got on the public-address system and apologized. It was unclear whether a rogue patron or an employee was responsible for the comment, but many customers expressed their anger to store management.