Whether or not it's legal to ask for a sperm from a specific race is besides the point. It's clearly immoral to have race as an option.
Why? I wouldn't say it's immoral for a woman to be able to decide whose sperm goes into her body, regardless of the factors she bases that decision on.
Plus, as others have pointed out, the kid's race will impact him/her as well as the mother. Unless you really don't want your kid to be white for whatever reason, there's no reason not to opt for a white guy's sperm if you live in a racist town.