“After I painted my nails, I had to see if the color-changing might occur if I just held my nails up to a lamp inside my house. Nope! I held one of my hands underneath a bright lamp for several minutes and no change it all. Then I decided to try immersing my hand in hot water to see if maybe heat would change the color. Nope! You really do have to be out in the sun for the change to occur. I think that’s pretty neat!