WordNet sense 1 ((used of color) artificially produced; not natural):

colored, coloured, dyed

WordNet sense 2 (contrived by art rather than nature):

artificial, unreal

WordNet sense 3 (having lost freshness or brilliance of color):

washed-out, washy, faded

WordNet sense 4 (weak in color; not colorful):

colorless, colourless