A pie’s turned a dark brown (5)
I believe the answer is:
sepia
'a dark brown' is the definition.
(I've seen this in another clue)
'a pie's turned' is the wordplay.
'turned' indicates anagramming the letters.
'a'+'pies'='apies'
'apies' anagrammed gives 'SEPIA'.
(Other definitions for sepia that I've seen before include "source of ink" , "Brownish tone associated with old photographs" , "Reddish-brown; cuttlefish ink" , "A greyish brown" , "Sort of drawing" .)