In 2009, undergraduates at the University of Cambridge worked with scientists and artists to engineer E. coli into E. chromi, a new type of bacteria that secretes a range of colorful pigments. The genetic 'BioBricks' responsible for color can be combined with other custom DNA sequences to achieve various useful effects. For instance, E. chromi could color feces blue in the presence of an intestinal disease, or turn red in response to arsenic in groundwater.
In future scenarios, the altered bacteria give rise to a new profession of chromonauts who search the earth for new organic pigments. The Orange Liberation Front, an imaginary Dutch terrorist organization, might even demand an end to patents on orange-generating genes. The above video, which won the Bio:Fiction prize for documentaries, is a fun look into some plausible (and less so) applications for a new piece of biotech. The technology used for E. chromi bacteria may open new areas for information decoration on a living canvas. Maybe transgenic humans will someday flush blue when they're feeling down, or cover up an actual yellow belly when they're being cowardly. I feel less enthusiastic, however, about rainbow-hued poop that marks every stomach bug.