There are many smart materials that have loads of different functions. Smart behaviour in a material occurs when a material can sense some stimulus from its environment and react to it. Smart materials are manufactured for their function and technical performance rather than the way they look.
Thermo chromic is one of the many colour changing materials. This material is designed to change colour at a particular temperature, the scientific term for this material is when a thermal stimulus causes a useful visual response. Many people own thermo chromic clothing and bath plugs that show when the water is too hot. Older types of thermo chromic materials were not good for the environment as they were made using mercury so they were poisonous.
Fluorescent materials produce both visible and invisible light. In daylight fluorescent pigments have a white or light colour, whereas under UV radiation they produce a intensive fluorescent colour.
Photo chromic materials are another type of colour changing material. The garments are colourless in a dark place, but when the sun shines on them ultraviolet radiation is applied the material changes and exhibits a new colour. Once the light source is removed the garment would return to its first state. They do not contain toxic substances.