The Collaborative International Dictionary of English v.0.48:

Discolor \Dis*col"or\, v. t. [imp. & p. p. Discolored; p. pr.
   & vb. n. Discoloring.] [OE. descolouren, OF. descolorer, F.
   d['e]colorer, fr. L. dis- + cololare, coloratum, to color,
   color color. See Color.] [Written also discolour.]
   1. To alter the natural hue or color of; to change to a
      different color; to stain; to tinge; as, a drop of wine
      will discolor water; silver is discolored by sea water.
      [1913 Webster]

   2. To alter the true complexion or appearance of; to put a
      false hue upon.
      [1913 Webster]

            To discolor all your ideas.           --Watts.
      [1913 Webster]

WordNet (r) 3.0 (2006):

discolor
    v 1: lose color or turn colorless; "The painting discolored"
         [ant: color, color in, colorise, colorize,
         colour, colour in, colourise, colourize]
    2: cause to lose or change color; "The detergent discolored my
       shirts"
    3: change color, often in an undesired manner; "The shirts
       discolored" [syn: discolor, discolour, colour, color]

Moby Thesaurus II by Grady Ward, 1.0:

116 Moby Thesaurus words for "discolor":
   achromatize, attaint, bedaub, besmear, besmirch, besmoke, bestain,
   blacken, blanch, blaze, blaze a trail, bleach, blemish, blot,
   blotch, blur, brand, chalk, chalk up, check, check off, cicatrize,
   dapple, dappled, darken, dash, daub, decolor, decolorize, defile,
   define, delimit, demarcate, dim, dirty, dot, drain, drain of color,
   dull, engrave, etiolate, fade, fleck, freckle, fume, gash, hatch,
   impress, imprint, line, make a mark, mark, mark off, mark out,
   motley, mottle, multicolor, multicolored, multihued, nick, notch,
   pale, parti-colored, pencil, pepper, peroxide, point, prick, print,
   punch, punctuate, puncture, riddle, scar, scarify, scorch, score,
   scotch, scratch, seal, seam, sear, singe, slubber, slur, smear,
   smirch, smoke, smut, soil, speck, speckle, splotch, spot, stain,
   stamp, stigmatize, streak, striate, stripe, sully, taint, tar,
   tarnish, tattoo, tick, tick off, tone down, trace, underline,
   underscore, varicolored, versicolor, versicolored, wash out,
   whiten