I've tried tinting epoxy with a little Testors paint, but I found something better. We have a Tap Plastics store close by, and they sell little bottles of epoxy tint for around $2.50. Its simply a pigment paste that you add while mixing your epoxy. I've used it with 6 and 30 minute as well as the finish epoxy. I have even mixed several colors to match Ultracoat. It slows the cure down a little depending on how much you add. You need to add more if you want the epoxy to be opaque.