How do I get my icing REALLY black without using chocolate frosting?
You could try making it brown first or some other dark color, and let it sit for a while too.
Agreeing with starting with brown icing. Also using Americolor Super Black gel should do it.
Wilton makes a really good gel food coloring in all kinds of colors. I bought the black the other day and it works great.
Here in the UK we have a colouring called Black Extra - I find that works quite well. By Sugarflair. It really does help to start with brown though.