Blue feathers (4)
I believe this clue is a double definition.
'blue' is the first definition.
(I've seen this before)
'feathers' is the second definition.
(down is a kind of feathers)
(Other definitions for down that I've seen before include "Not working (computer)", "Rolling hill; soft feathers", "Depressed; swallow", "when in adversity", "In a low mood; hill".)