Sciffy generally doesn't do too well in that regard. Eureka is the exception, as far as I know, although there are a couple of shows that I don't watch.
Well, Agam Darshi in Sanctuary seasons two and three was a main character in a series with a very small cast.
Stargate SG-1 had Chris Judge of course in a major role but it also of course made him the taciturn the character. SG-1's captains and generals, pretty much everybody in fact, were not just white but Anglo-Saxon. The only major exceptions I recall were the merely Saxon General Bauer and Steven C. Williams' General Vidrine.
Overall I'd have to agree that Syfy is pretty conservative.
But these things are really hard to judge without doing boring statistics that are also difficult statistics. CBS by and large is pretty white, but one of its biggest shows, CSI, had Lawrence Fishburne in the lead, which must count for more than an African-American friend.