Antonyms of verb whiten

1 sense of whiten

Sense 1
whiten, white -- (turn white; "This detergent will whiten your laundry")
       Antonym of blacken (Sense 1)
      => blacken, melanize, melanise, nigrify, black -- (make or become black; "The smoke blackened the ceiling"; "The ceiling blackened")

Synonyms/Hypernyms (Ordered by Estimated Frequency) of verb whiten

1 sense of whiten

Sense 1
whiten, white -- (turn white; "This detergent will whiten your laundry")
       => discolor, discolour, colour, color -- (change color, often in an undesired manner; "The shirts discolored")