The Black Killer Bugger is a cross between a Killer Bug and a Woolly bugger. The Killer Bug is a scud imitation, but in larger sizes it also imitates a crane fly larva. the Woolly Bugger was originally tied as a hellgrammite imitation. The yarn body and marabou tail makes a very simple, very effective fly. It could be a hellgrammite, it could be a leech, it could be a very dark minnow. To the fish, it looks like food.
Black was chosen because I once read an article that said you could catch anything on a black Woolly Bugger. I have tried other colors, but none were better than black.