Is pea changing colour? (5)
I believe the answer is:
sepia
'colour?' is the definition.
(sepia is a kind of colour)
'is pea changing' is the wordplay.
'changing' is an anagram indicator.
'is'+'pea'='ispea'
'ispea' anagrammed gives 'SEPIA'.
(Other definitions for sepia that I've seen before include "brownish colour" , "Reddish brown -- ie sap (anag)" , "Denizen of deep" , "Reddish-brown colour - easy as pie" , "Brown with a red tinge" .)