a kind of deep blue, one of the seven prismatic colors.-a blue dyestuff obtained from several plants belonging to very different genera and orders; as, the woad, isatis tinctoria, indigofera tinctoria, i. anil, nereum tinctorium, etc. it is a dark blue earthy substance, tasteless and odorless, with a copper-violet luster when rubbed. indigo does not exist in the plants as such, but is obtained by decomposition of the glycoside indican.-having the color of, pertaining to, or derived from, indigo.