Rainbows are mirrors that reflect others back on themselves. While they may reflect there is an absorption that occurs. When a pigment absorbs a photon of light, it becomes excited. This means it has extra energy making it no longer normal. On a subatomic level it goes through excitation. This is when an electron is bumped into a higher energy orbit. This doesn’t always just occur. It takes a photon with just the right amount of energy to bump an electron, in between orbitals in a way that can excite a pigment. When a pigment becomes excited it becomes unstable. To stabilize it may transfer this extra energy. As above so below.