The Collaborative International Dictionary of English v.0.48:

Dichroism \Di"chro*ism\, n. [Gr. ? two-colored; di- = di`s-
   twice + ? color.] (Opt.)
   The property of presenting different colors by transmitted
   light, when viewed in two different directions, the colors
   being unlike in the direction of unlike or unequal axes.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dichroism
    n 1: pleochroism of a crystal so that it exhibits two different
         colors when viewed from two different directions