2,6-dichlorophenolindophenol sodium salt is a redox dye commonly used as a monitor of the light reactions in photosynthesis because it is an electron acceptor that is blue when oxidized and colorless when reduced. It is part of the Hill reagents family. DCPIP can also be used as an indicator for Vitamin C. If vitamin C, which is a good reducing agent, is present, the blue dye, which turns pink in acid conditions, is reduced to a colorless compound by ascorbic acid.