The vibrant colours seen on butterfly wings or peacock feathers are examples of structural coloration, which occurs when micro- or nanoscale structured surfaces interfere with visible light. In this week’s issue, Lauren Zarzar and her colleagues reveal a previously unrecognized mechanism for generating structural iridescent colour from droplets of colourless liquid. The researchers found that micrometre-scale droplets suspended on the back of a transparent Petri dish, or multiphase droplets, reflect coloured light from their edges when illuminated with a beam of white light. The effect is not produced by material dispersion, as might be thought, but by an optical phenomenon based on interference of light that undergoes total internal reflection along the curved surface of the droplet. By varying the length and curvature of this interface, the researchers were able to control the colours generated, and by patterning droplets in a 2D array they managed to create pixelated images.