Structural Colour and Iridescence

A green bottle. © Eugene Brennan

A species of green bottle I think. Sorry quality not the best. Normally the way colour works is that if an object is illuminated by light, pigment in the surface absorbs some wavelengths and reflects others. The Sun mostly produces broad spectrum white light, so a red rose looks red because it absorbs all the colours of the rainbow in white light and only reflects red. Some animals, insects and plants have evolved so they can produce structural colour on their body's surface which doesn't rely on pigments. Instead, the topography of the surface is such that tiny elements like ridges or other structures, having dimensions comparable to the wavelength of light, produce iridescent colours. Iridescence is a phenomenon that makes soap bubbles, oil spilled on a wet road, opals and the underside of CDs look colourful. It's caused by wave interference where waves of light combine and the peaks and troughs add or subtract from each other to reinforce certain wavelengths, making colours emerge from white light. Beetles, blue and green bottles, some butterflies and starlings are examples of animals that use iridescence. The theory is that it confuses predators or is used for communication.