Colour of pie changed when covered in it (5)
I believe the answer is:
sepia
'colour' is the definition.
(I know that sepia is a type of brown)
'pie changed when covered in it' is the wordplay.
'changed' indicates an anagram.
'when covered in' indicates putting letters inside.
'it' becomes 'sa' (old-fashioned abbreviation for sex appeal).
'pie' anagrammed gives 'epi'.
'epi' put into 'sa' is 'SEPIA'.
'of' acts as a link.
(Other definitions for sepia that I've seen before include "Brown with a red tinge" , "Denizen of deep" , "Rich reddish-brown colour" , "Brown of old photos" , "Brown colour of old photo" .)