WordNet sense 1 ((of color) discolored by impurities; not bright and clear):

muddy, muddied

WordNet sense 2 (combined with extraneous elements):

impure

WordNet sense 3 (thickly covered with ingrained dirt or soot):

grimy, grubby, grungy, raunchy, begrimed

WordNet sense 4 (soiled or likely to soil with dirt or grime):

dirty, unclean, soiled

WordNet sense 5 (causing dejection):

blue, dark, depressing, disconsolate, dismal, drab, drear, dreary, gloomy, grim, sorry, dispiriting

WordNet sense 6 (lacking cheer; depressing):

cheerless, uncheerful