WordWeb Online

1. Lacking in variety and interest
   "a colourless and unimaginative person"; "a colourless description of the parade"
   - colorless [US]
    
2. Weak in colour; not colourful
   - colorless [US]

See also: achromatic, ashen, blanched, bleached, bloodless, color [US], colour [Brit, Cdn], colourlessness [Brit, Cdn], drab, dull, dulled, etiolate, etiolated, faded, grayed [US], greyed [Brit, Cdn], hebetudinous, livid, lurid, neutral, pale, pallid, pastelike, pasty, prefaded, sober, somber [US], sombre [Brit, Cdn], vividness, wan, washed-out, washy, waxen, waxlike, waxy, white, whitened

Antonym: colourful [Brit, Cdn]

Encyclopedia: Colourless