Hairy ape is a brownish colour (5)
I believe the answer is:
sepia
'a brownish colour' is the definition.
(I've seen this before)
'hairy ape is' is the wordplay.
'hairy' indicates an anagram (hairy can mean difficult or tricky).
'ape'+'is'='apeis'
'apeis' with letters rearranged gives 'SEPIA'.
(Other definitions for sepia that I've seen before include "Colour of old photographs" , "Pigment got from cuttlefish ink" , "source of ink" , "Sort of drawing" , "Reddish brown -- ie sap (anag)" .)