Why does it seem like I know so many more outwardly racist black people towards whites?

I have about 300 co-workers, with all types of ethnic groups, asian, hispanics, blacks, whites, Native American, East Indian and Africans. There is one person in particular who recently confronted me with all kinds of accusations implying that I am a racist (I am white, she black), even though I have never done or said anything racist in my life. What she doesn't know is that I have a Japanese wife and therefore our son is of mixed ehtnicity, so I am very aware of discrimination and make every effort not to partake in it. Anyway, her basis for the accusations is that I never talk to her and that I mostly socialize with white co-workers. However, the reason I avoid her is because she is basically crazy and a trouble maker. I have always felt like there is a real atmosphere of hostility coming from the majority of my black co-workers, I have heard comments in the bathroom like, "All white people are the devil," and I have been flat out ignored by some when I say hello to them.