Is pea changing colour? (5)
I believe the answer is:
sepia
'colour?' is the definition.
(I know that sepia is a type of pigment)
'is pea changing' is the wordplay.
'changing' indicates an anagram.
'is'+'pea'='ispea'
'ispea' with letters rearranged 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" .)