can anyone tell me, what the secret is to getting true black icing...... Do you start out using chocolate buttercream and then add black gel coloring?

1 - do NOT use Wilton colors. Americolor, Chefmaster, and CK are the brands to use.
2 - you have to use a LOT more of the black (same for red) to get it dark enough
3 - remember that colors deepen with time. I have found that if I get my black to a dark gray, by the time the cake is eaten/delivered it has "matured" to a nice black.
4 - yes, starting with chocolate buttercream helps!

I use chefmaster.. And I put lots. Here is a tutorial on making brown, but is the same way with black.

I have used wilton colors and find them to be ok but the secret to making black or red is to start with a tinted or dark base to begin with

Chocolate would be the way to go for a base

Hello - just stopping by CC for a visit and thought I'd help answer your question.

I start out by adding equal amounts of (red and blue) or (green and blue) or (red and green) till you get a truly ugly color then start adding black alone then you don't have to add the whole bottle. I use Americolor. Works with fondant or BC.

http://www.cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1309691