The Collaborative International Dictionary of English v.0.48:

Indigo \In"di*go\, a.
   Having the color of, pertaining to, or derived from, indigo.
   [1913 Webster]

   Indigo berry (Bot.), the fruit of the West Indian shrub
      Randia aculeata, used as a blue dye.

   Indigo bird (Zool.), 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 Indigofera tinctoria, or common
      indigo plant, the Indigofera Anil, a larger species,
      and the Indigofera 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 (Zool.), 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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Indigotin \In"di*go*tin\, n. (Chem.)
   See Indigo blue, under Indigo.
   [1913 Webster]

WordNet (r) 3.0 (2006):

indigotin
    n 1: a blue dye obtained from plants or made synthetically [syn:
         anil, indigo, indigotin]