Indigo is one of the oldest known dyes. Indigo, the compound that yields indigo blue, is a glycoside: a sugar (a form of glucose) bound to another molecule, indoxyl.
Ancient Egyptians, Greeks and Romans used indigo as eye shadow, crayons, and paint as well as for coloring fabric. Its use also dates back to ancient Japan and West Africa over 5000 years ago. In Europe the woad plant (Isatis tinctoria) was used to obtain a blue dye. The dye chemical extracted from woad is indigo, the same dye extracted from "true indigo", Indigofera tinctoria, but in a lower concentration. “True indigo”, Indigofera is a member of the Leguminosae family- relative of beans, peas and peanuts. Many plants will yield indigo but only a few in sufficient quantity to be of any use in dyeing.