Yellow photochromic pigment changes color when exposed to sunlight. A white powder at night & indoors that turns a bright yellow minutes after sunlight exposure. Its colorless state can appear transparent when mixed at lower ratios with mediums such as paint, resin, acrylic or plastic. Note: Unlike some other photochromic powders, yellow is not very reactive to UV or black lights. It is best used when a color change is expected outdoors as it is most reactive to direct sunlight.