The Collaborative International Dictionary of English v.0.48:

Euchroic \Eu*chro"ic\, a. [Gr. ? well-colored; e'y^ well + ?
   color.] (Chem.)
   Having a fine color.
   [1913 Webster]

   Euchroic acid (Chem.), an organic, imide acid, obtained as
      a colorless crystalline substance, C12H4N2O8 by heating
      an ammonium salt of mellitic acid. By reduction it is
      changed to a dark blue substance (euchrone), -- hence its
      name.
      [1913 Webster]