I've got some beads that will change color under sunlight. The stronger the intensity of sunlight, the darker (purple) the beads will turn. If the beads are put back indoor, they will resume their original color (white) after a while. The beads will also change color if they're under the light from a UV torch. The beads are plastic like. I tried to cover the beads with cellophane of different colours (red, yellow, green, and blue) and put them under the sun. After a while, when I uncovered the cellophane, I found that the beads covered with the blue cellophane became the darkest while the beads covered with yellow/ green cellophane had become only light purple, and the color of the beads covered with red cellophane were somewhat in between. I did have a control with beads not covered, the beads didn't become as dark as those covered by blue cellophane but were slightly darker than those covered by red cellophane. Can anyone help me explain my observation? Is it because there are different ranges of light penetrating the cellophane? Or is it because cellophane of different colors absorb different ranges of light in sunlight?