Diffraction Grating

A diffraction grating is a type of structure that produces coloration via structural color. The spacing of the diffraction grating (w in diagram below) must be about equal to the wavelength of light in the visible range (400-700nm). With that, the different wavelengths of visible light will be diffracted in different directions. With a simple diffraction grating, as shown, an observer will see a different color depending on the angles of incidence of the incoming beam and their perspective.

The existence of diffraction gratings in some fossils 300 million years ago, which infer structural color, also infer that there existed some animals that responded to color (predator, prey or the animal itself), so supposes the existence of color vision. The diffraction gratings would have no purpose and therefore not have evolved if there were no animals that had color vision.