The Collaborative International Dictionary of English v.0.48:

Decolorize \De*col"or*ize\, v. t.
   To deprive of color; to whiten. --Turner. --
   De*col`or*i*za"tion, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

decolorize
    v 1: remove color from; "The sun bleached the red shirt" [syn:
         bleach, bleach out, decolor, decolour,
         decolorize, decolourize, decolorise, decolourise,
         discolorize, discolourise, discolorise]