Slowly stir one color of powder into the resin mixture in each of the two mixing cups. You would have to add A LOT more glow powder before you caused any problems with the resin's ability to cure. Once the two colors are mixed, it's time to pour them into your mold.
Glow in the Dark Powder Daytime colors have a fluorescent pigment tint added to the natural glow pigment for a splash of color. The pigment makes its way into the crevices and leaves a layer of resin above that can be planed, sanded, or buffed without losing pigment in the process.