indigo

(noun) a blue dye obtained from plants or made synthetically. Synonyms: anil, indigotin.

(noun) deciduous subshrub of southeastern Asia having pinnate leaves and clusters of red or purple flowers; a source of indigo dye. Synonyms: indigo plant, Indigofera tinctoria.

(noun) a blue-violet color.

(adj) having a color between blue and violet. Example: "Indigo flowers."