The use of color is key in microbiology, especially for identification of bacteria. For example, Bromocresol purple is a pH indicator that turns yellow in the presence of lactose-fermenting bacteria. Pictured here is the brilliant contrast of lactose-fermenting Enterobacteriaceae on the purple agar.
Unexpectedly, a mysterious fungus also appeared on this plate, making itself known with a bright green hue. The colors produced by fungi are due to a mixture of chemicals produced as waste, metabolites, digestive agents, or toxins. The exact reason why certain molds produce certain colors is unknown, which perhaps makes their beauty even more captivating.