shopmaninc.com sells liquid colored pigments that work for polyester, gelcoats, epoxy, and some urethanes. Who knows what the liquid medium is? My guess is that it is oil.

Another company sells pigment that is dispersed in epoxy resin:

http://www.raka.com/Accessories.html

If I add a small amount of the pigmented epoxy resin from raka.com to the US Composites epoxy resin from shopmaninc.com, will there be any compatability problem? I am inclined to buy the raka.com stuff, since I know it is epoxy resin that will harden in the final cure and not an oil-based paste. Maybe this is an important detail, maybe not. Any thoughts?