Wilton Chocolate ercream... how much cocoa do I add?

Eh, I just keep adding cocoa until I get the color I want, then I put in the rest of the powdered sugar. Maybe half a cup or so. I've never done the Wilton cl, but that always works for me. Since you're doing black, there's no reason you can't use real er instead of shortening (blech) and er flavor (extra blech). Honestly, er doesn't add *that* much color to ercream. I use er for my whites too.