The Collaborative International Dictionary of English v.0.48:

achromatise \achromatise\ v.
   1. remove color from.

   Syn: achromatize, make achromatic
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Achromatize \A*chro"ma*tize\, v. t. [imp. & p. p.
   Achromatized; p. pr. & vb. n. Achromatizing.] [Gr. 'a
   priv. + ? color.]
   To deprive of color; to make achromatic. [Also spelled
   achromatise.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

achromatise
    v 1: remove color from; "achromatize the lenses" [syn:
         achromatize, achromatise]