To get the great color, you just need to sand the blank side of the game tiles a little. Wipe off dust. Put in pot with some tea bags or coffee grounds. I put in lots of coffee grounds. Put in enough water to cover the tiles and then some. Let boil and keep to low boil 45 minutes to an hour. Stir periodically. Check the color. Some will color better than others. Rinse, let cool, and dry them off with a towel. Stamp on them with permanent ink.
I have also tried it with herbal tea and have gotten the greatest burgundy/plum colors. You want the water concentrated with tea or coffee so the game tiles will stain.