just like you use paste color to paint on fondant? I have a LARGE area, (12" circle), i need to be black. I dont have a lot of chocolate color so my question is after I take my 12" circle out of the pan. The cake pan is my mold, can I paint with the candy color. Or will it look streaky?

Instead of coloring the whole batch of chocolate.

I would color the whole batch first. I have painted small areas with the colorant but it wasn't as clean as I hoped. I find painting on chocolate is best done with cocoa butter paints, they too though won't provide a clean look if you are painting a whole cake. This is just my experience with these colors.