<p>Organisms possess a diversity of colours to promote their survival and reproductive success, using various mechanisms, including pigmentation, bioluminescence and structural colouration. These colouration strategies serve crucial ecological functions, such as crypsis for camouflage, aposematism for predator deterrence and vibrant displays that attract pollinators and potential mates. In particular, the ability to dynamically alter colour in response to environmental stimuli allows organisms to rapidly modify their appearance for communication, predation and defence. Drawing inspiration from these natural phenomena, dynamic colour change systems can be designed for applications in optics, sensors and biomedicine. In this Review, we discuss the biological mechanisms driving natural colouration and dynamic colour change, outlining how these can be recreated in engineered systems using structured materials, such as photonic crystals, liquid crystals, metasurfaces and thin films. We highlight how artificial dynamic colour systems can be designed to respond to different stimuli, such as mechanical, electrical, chemical, thermal and magnetic stimuli, examining their application in various fields, including in biomedical devices, sensing and displays.</p>