Same word as dimmest:

blah, bleary, blurred, caliginous,cloudy,dark,dingy,dreary,dull,dusk, dusky,faded,faint,flat,fuzzy,gloomy,gray, ill-defined,indistinct,lackluster, lightless, mat, monotone,monotonous,murky, muted, obscured,opaque, overcast,pale, poorly lit, shadowy, sulli