errrm, there are two black riders in this years tour.
Zakayo Ndbri and Mwangi Samwel as far as I know. Both Kenyan.
As above, any team who can find a rider who is lightning fast will pick them up, they really won't care about their skin colour. If they can win races then they've got a job. Plus, any team that is seen to be supporting black men know they will gets loads of positive feedback so they'll most probably be actively looking for black riders.
Why black men are not attracted to road racing is an entirely different matter and one that I personally think is based in history and culture. I don't think the black community in Europe or America are particularly drawn to road racing as a sport what with football and rugby being far more prominent/financially sound.
Maybe you should stand as an embassador eth3r, perhaps a black man would draw more support and encouragement to give it a try. One area that I reckon is a good starting point is track riding. The Manchester Velodrome is located right in the middle of a large black community yet no black riders ride the track (that I've seen and I'm there quite a bit) and Bauge at the very least has shown us that black riders can excel in such an arena.