"Black Widowmaker"?
I would suggest "Black Betty", but I think that one's already taken.
Other suggestion I've got as a sort of pun is "Traveller", after Robert E. Lee's semi-famous war horse. Downside there is you might get mistaken as one of those Southerners who still mourns losing the Civil War. But if you can find any other well-known war horses, they would work in the same way. "Silver"? Now that would screw with people.