Photochromic Pigments react to changes in light levels, they are so quick-changing that they will completely change from their pale color to a deep beautiful rich color within 1 second of being exposed to direct sunlight. <br> This is a great color change product for those who live in any climate, as they only need sunlight to change. Photochromic pigments will not fade in UV light, as they are dependent on UV for activation.