WordNet sense 1 (overly diluted; thin and insipid):

watery, weak

WordNet sense 2 (reduced in strength or concentration or quality or purity):

dilute, diluted

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

washed-out, bleached, faded

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

colorless, colourless