I don't think there is a LOT of difference between black and white crappie. When you are on the edge of disaster, I suppose any improvement the black supposedly offer can be helpful. If you religiously do corrective fishing in a small pond, I don't think it matters that much.
Adding fish from another pond is a questionable practice with bream, because undesirable crossbreeding is so common. However crappie don't present that problem. I've even read somewhere that black/white crosses can produce some big robust fish.
