orcein

from The Century Dictionary.

• noun A nitrogenous compound (C₇H₇NO₃) formed from orcine and ammonia.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) A reddish brown amorphous dyestuff, C7H7NO3, obtained from orcin, and forming the essential coloring matter of cudbear and archil. It is closely related to litmus.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry a dye, related to litmus, that is extracted from the lichen Rocella tinctoria; used as a microscopic stain and as a food colouring