I am making black icing using Indydebi's buttercream recipe (yum).  I added americolor super black. I then read on CC that some started with chocolate icing base. Is it too late to add cocoa since color is already in?  Also will just adding cocoa to this recipe make it a true chocolate icing or should I use another recipe?  TIA!

try adding one square at a time of Melted Unsweetened Bakers Chocolate from the grocery store.

in place of adding cocoa powder.

if you decide to make a new batch properly, this batch can be frozen and used another time, icing never need go to waste.  good luck.