Brilliant iridescent fish scales change colour depending on the angle from which you look at them. The very word is from the greek word iris meaning rainbow.
Inspired by the fish scale iridescence, scientists have developed a graphene coating that changes colour when deformed. It could provide an early warning of hidden structural damage in buildings, bridges and vehicles.
By overlapping graphene nanoplatelets, the researchers achieved unique fish scale like structures. Under stress, the layers compress and change the colour of reflected light.
Variable structural colouration of composite interphases Yinhu Deng et al, Mater. Horiz., 2017