I just had a lady order a 4 tier IMBC cake with a lot of black piping on it, which I'll probably do in royal icing. I've never had my colored piping bleed (but I've never done black ). It seems like it should be fine, but I have to ask anyway:
Has anyone done this combo, and have you had any bleeding?
I've done black on white powdered sugar buttercream. It was fine. I do know that putting it in the fridge might cause it to bleed because of the condensation that forms.
In that case, since IMBC should be refrigerated, you might have a problem.
I agree on IMBC it will probably bleed. And depending on the black you use it will bleed purple/black or green/black or other. Why don't you make a little test sample? Sounds gorgeous.