The pigment is a nontoxic alternative to cadmium sulfide pigments. Phycoerythrin is an accessory pigment to the main chlorophyll pigments responsible for photosynthesis. Zinc sulfate is a chemical in dyes and pigments. Biochromes are colors chemically formed microscopic, natural pigments. Dark skin is a human skin color that is rich in melanin pigments, especially eumelanin. Coloration is produced from both red pigments and yellow carotenoid pigments. The earliest known pigments were natural minerals. The two pigments are highly acidic compounds. Castavinols are another class of colorless molecules derived from colored anthocyanin pigments. The color of purple varieties is due to various anthocyanin pigments. Intestinal anaerobic bacteria transform haemoglobin into sulfhemoglobin and other colored pigments. They have various functions such as storage of reserves, excretory materials, pigments, and minerals. Umber is darker than the other similar earth pigments, ochre and sienna. All natural hair colors are the result of two types of hair pigments. Absorption of light by photosynthetic pigments converts photons into chemical energy.