Plasti-cote is supposedly robust (at least some of their products, anyway). One of the versions with a plasticizer, like for exterior plastic bumpers, would seem appropriate.
Actually getting plastic, which usually has the color pigment in the plastic itself, to change color by dying seems unlikely. Usually staining occurs when you don't want it to happen.
Benchmade, afterall, uses coatings for many of its alternative colored Grips for a reason, I'd think; and the coating chips.