noun A greenish dark blue color; the color of indigo dye.
indigo:
noun A blue-colored dye obtained from certain plants (indigo plant or woad), or a similar synthetic dye.
noun An indigo plant, such as from species in genera Indigofera, Amorpha (false indigo), Baptisia (wild indigo), and Psorothamnus and Dalea (indigo bush).