"INDIGO" -Photograph of crystalline citric acid found in citrus fruit"Indigo" is a photograph of citric acid crystals., which I grew by evaporation on a glass microscope slide. Citric acid is found naturally in citrus fruits and is an antioxidant. This photograph was taken through a microscope and the crystal facets create the colors naturally by refracting transmitted white light, separating it into the colors of the spectrum.