What is stealth racism?

Racists do not necessarily admit their true motives. So, if you don't want to hire African-Americans, for example, you don't have to say that you didn't hire a given applicant because of his ethnicity, you can claim that he isn't the most qualified applicant. It can be very difficult to prove otherwise. Still, if you have a hundred employees and they are all of European descent, it is going to look very suspicious.