How to color the concrete screed (ala cube)?

I bought a high quality impregnation (Deep Coat V) hoping that it would make a "wet cube" effect. I have impregnated a small piece for a trial, but the effect is disappointing. Will any coloring impregnate work? if so, do you have any checked? The photo below does not reflect this, but the cube is very light for the most part, and only dark here and there. The goal is to give a dark, reasonably uniform color and to impregnate the ankle at the same time. Do you have any ideas? I know I could have put the dye straight into the cement mixer, but I screwed it up and now I want to fix it.