Green? Might be a vine (5)
I believe the answer is:
naive
'green?' is the definition.
(green can mean naive or innocent)
'might be a vine' is the wordplay.
'might be' indicates an anagram (I've seen this in other clues).
'a'+'vine'='avine'
'avine' anagrammed gives 'NAIVE'.
(Other definitions for naive that I've seen before include "Unenlightened" , "Rather too innocent and trusting" , "Showing lack of experience or sophistication" , "Simple, innocent or unsophisticated" , "Lacking guile" .)