1. [n]  a blue-violet color
2. [n]  deciduous subshrub of southeastern Asia having pinnate leaves and clusters of red or purple flowers; a source of indigo dye
3. [n]  a blue dye obtained from plants or made synthetically

Indigo
Indigo: Music For Exploration And Evolution

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1. \In"di*go\, n.; pl. {Indigoes}. [F. indigo, Sp. indigo,
   indico, L. indicum indigo, fr. Indicus Indian. See {Indian}.]
   1. A kind of deep blue, one of the seven prismatic colors.
   2. (Chem.) 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.
   Note: Commercial indigo contains the essential coloring
         principle indigo blue or indigotine, with several other
         dyes; as, indigo red, indigo brown, etc., and various
         impurities. Indigo is insoluble in ordinary reagents,
         with the exception of strong sulphuric acid.
   {Chinese indigo} (Bot.), {Isatis indigotica}, a kind of woad.
   {Wild indigo} (Bot.), the American herb {Baptisia tinctoria}
      which yields a poor quality of indigo, as do several other
      species of the same genus.
   

2. \In"di*go\, a.
   Having the color of, pertaining to, or derived from, indigo.
   {Indigo berry} (Bot.), the fruit of the West Indian shrub
      {Randia aculeata}, used as a blue dye.
   {Indigo bird} (Zo["o]l.), a small North American finch
      ({Cyanospiza cyanea}). The male is indigo blue in color.
      Called also {indigo bunting}.
   {Indigo blue}.
   (a) The essential coloring material of commercial indigo,
       from which it is obtained as a dark blue earthy powder,
       with a reddish luster, {C16H10N2O2}, which may be
       crystallized by sublimation. Indigo blue is also made
       from artificial amido cinnamic acid, and from artificial
       isatine; and these methods are of great commercial
       importance. Called also {indigotin}.
   (b) A dark, dull blue color like the indigo of commerce.
   {Indigo brown} (Chem.), a brown resinous substance found in
      crude indigo.
   {Indigo copper} (Min.), covellite.
   {Indigo green}, a green obtained from indigo.
   {Indigo plant} (Bot.), a leguminous plant of several species
      (genus {Indigofera}), from which indigo is prepared. The
      different varieties are natives of Asia, Africa, and
      America. Several species are cultivated, of which the most
      important are the {I. tinctoria}, or common indigo plant,
      the {I. Anil}, a larger species, and the {I. disperma}.
   {Indigo purple}, a purple obtained from indigo.
   {Indigo red}, a dyestuff, isomeric with indigo blue, obtained
      from crude indigo as a dark brown amorphous powder.
   {Indigo snake} (Zo["o]l.), the gopher snake.
   {Indigo white}, a white crystalline powder obtained by
      reduction from indigo blue, and by oxidation easily
      changed back to it; -- called also {indigogen}.
   {Indigo yellow}, a substance obtained from indigo.