Chameleon-Like ‘Opal’ Can Take on Any Colour

A new material could give a chameleon a run for its money — it can rapidly change colour to match that of any in the visible spectrum. The synthetic material can be likened to an opal, a mineral that owes its variety of colours to its layered structure: regions with a high refractive index, in which light travels slowly, are interleaved with regions with a low refractive index. Light waves with a wavelength — or colour — similar to that of the space between layers are scattered in a way that gives opal its iridescent sheen