Possibly ape is reddish-brown (5)
I believe the answer is:
sepia
'reddish-brown' is the definition.
(I've seen this before)
'possibly ape is' is the wordplay.
'possibly' indicates an anagram.
'ape'+'is'='apeis'
'apeis' with letters rearranged gives 'SEPIA'.
(Other definitions for sepia that I've seen before include "Colour from cuttlefish ink" , "Sort of ink" , "Colour of old photographs" , "Brown pigment produced from cuttlefish ink" , "cuttle" .)