Irisation or iridescence in super-cooled cloud droplets in cirrocumulus. Iridescence is an optical phenomenon of surfaces in which hue changes in correspondence with the angle from which a surface is viewed. Iridescence is often caused by multiple reflections from two or more semi-transparent surfaces in which phase shift and interference of the reflections modulates the incidental light (by amplifying or attenuating some frequencies more than others). In meteorology, irisation, is a type of photometeor, is multiple mixed iridescent colors caused by sunlight being diffracted in clouds. The colors are often brilliant and mingled together, sometimes similar to mother-of-pearl.