A vine turns green (5)
I believe the answer is:
naive
'green' is the definition.
(green can mean naive or innocent)
'a vine turns' is the wordplay.
'turns' indicates anagramming the letters.
'a'+'vine'='avine'
'avine' anagrammed gives 'NAIVE'.
(Other definitions for naive that I've seen before include "Too innocent or gullible" , "Simple in style or behaviour" , "Natural, unaffected" , "Innocent or not worldly enough" , "Lack of experience, innocent" .)