Hello, Actually I have tried that with a couple customers in the past. Thing is, the stain never seems to penetrate deep enough into the motar. naturally, if a different colors is wanted it is mixed into the motar when its wet at time of installation, and is color through. Maybe try some on a small area first, let it set a few weeks and see what you think. In both experience that I have done for my customers they both knew there was a chance it not looking right or lasting long, and we were righ. The stain never acheived the correct color they desired and it faded in one yr time. "Dont fix it if it aint broke"
Good Luck GregC