Colour Made by Structure
Iridescence is colour that changes with the angle of light or the viewer. It is often produced by microscopic structures that reflect and interfere with light rather than by pigment alone. The effect can make the scales of a sunbeam snake or rainbow boa appear to flash through several colours in direct light, even though the animal is not changing pigment from one moment to the next.
Not Every Shiny Scale Is the Same
Reptile skin includes a range of microscopic surface features and internal reflective cells. In snakes, scale nanostructures can influence sheen, water repellence and, in some species, structural iridescence. Chameleons use specialised iridophores within the skin for some colour effects. It is inaccurate to say that every reptile scale contains the same crystals or creates colour by the same process.
Function Must Be Tested Species by Species
Structural colour may affect camouflage, signalling or heat exchange, but a plausible function is not proof of one. The visual systems of predators, prey and mates differ from our own, and the effect changes with light angle and habitat. Iridescence is striking to observe, yet it should not encourage collecting wild reptiles or handling them for a closer view.
