The Collaborative International Dictionary of English v.0.48:

Decolor \De*col"or\, v. t. [Cf. F. d['e]colorer, L. decolorare.
   Cf. Discolor.]
   To deprive of color; to bleach.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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