Del Sol’s unique Sol Putty changes from Green to Purple with sunlight. The nontoxic, all-organic formula does not stain and is water soluble. It smells good, too!. Colors adjust back and forth in seconds! Even on a cloudy day, 80% of the suns UV rays still pass through the clouds, making your Del Sol Putty change!. Each putty canister comes with Del Sol’s safe, proprietary UV-LED light that lets you draw pictures, letters or whatever on the Sol Putty using this light. Hours of fun under the sun!. Spectrachrome Crystals reveal hidden colors when exposed to ultraviolet waves. When exposed to sunlight, the crystal has an energy-shift causing the color of the dye to become visible to the human eye.