Colour of an apple (6)
I believe the answer is:
russet
This clue is a double definition.
'colour' is the first definition.
(I know that russet is a colour)
'an apple' is the second definition.
(a russet-coloured apple)
'of' acts as a link.
(Other definitions for russet that I've seen before include "Brown with a reddish tinge" , "browny-red" , "Dessert apple" , "Autumnal red as of leaves" , "Brownish-red apple" .)