Reactive shirts made of 100% cotton with a special Aerochromic dye that reacts to elements in the air and changes color from black to white.
https://docs.google.com/a/macalester.edu/presentation/d/1DQxHrGI_IMQYewVSKoU168TiJT3ppzrtXGfjOvwmq4I/edit?usp=sharing