Bands of iridescent colours imaged by David Tiller (slide show). Iridescence in clouds is produced by interference of light waves scattered by individual tiny water droplets. We see the colours best in wave clouds when the droplets all form at the same time and have similar sizes. The millions of droplets then each produce the same colour. Similar colours in oily puddles or soap bubbles are generated differently. They come from interference between light waves scattered from the two surfaces of the oil or soap film. Image ©David Tiler , shown with permission.