The Collaborative International Dictionary of English v.0.48:

Dichromic \Di*chro"mic\, a. [Gr. ? two-colored; di- = di`s-
   twice + ? color.]
   Furnishing or giving two colors; -- said of defective vision,
   in which all the compound colors are resolvable into two
   elements instead of three. --Sir J. Herschel.
   [1913 Webster]