Lose colour (6)
(Other definitions for whiten that I've seen before include "Blanch" , "free from guilt" , "Become less colourful" , "New hit (anag.)" , "Bleach" .)
'lose colour' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for fade that I've seen before include "Discolour" , "Gradually grow faint" , "Lose brightness" , "Grow paler" , "Grow dull" .)