1) Atmospheric optical phenomena 2) Iridescence 
In meteorology, irisation, 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. They sometimes appear as bands parallel to the edge of the clouds. Irisation is caused by very uniform water droplets diffrac...
the effect or quality of being iridescent; iridescence.