Six slices no use, having turned green? (7)
I believe the answer is:
envious
'green?' is the definition.
(green with envy)
'six slices no use having turned' is the wordplay.
'six' becomes 'VI' (Roman numerals).
'slices' means one lot of letters goes inside another (inserted letters slice their way in).
'having turned' indicates anagramming the letters (letters turned into something else).
'no'+'use'='nouse'
'nouse' with letters rearranged gives 'enous'.
'vi' put inside 'enous' is 'ENVIOUS'.
(Other definitions for envious that I've seen before include "Begrudging another's fortune" , "Feeling jealousy" , "Full of jealousy" , "Oi, Venus (anag.)" , "Covetous, jealous" .)