Dahmer's the most 'colour-blind' serial killer (whites, blacks, asians, even a hispanic iirc). Even then, it was not about race to him. His neighbourhood was not predominantly white. Not only were non-whites readily available, he had non-suspicious access to them. (ps: I think it was about physical attributes. He had a thing for lean torsos and limbs).

So again, it's more of availability of victims and whether they can get away with it.