These opaque pigments work great to color Ice Resin, Castin Craft Clear Resin, Devcon 2 Part Epoxy and more!

You can color UV resin with transparent colorants.  UV resin works best without colorant of any kind.  This is because UV light is the curing agent.  If the light cannot penetrate the resin, it cannot cure the resin.  You may also have to cure each side of the resin or cure very thin layers of the resin.  

Opaque colorants only work if applied in very very thin layers.  This is far more difficult to achieve as the light is the curing agent with UV resins.  I recommend not coloring the resin with opaque.  It can be done, but the layers have to be cured individually and they have to be the thickness of a paint swipe with a brush or sponged on.