Green paper assimilated by church body (5)
I believe the answer is:
naive
'green' is the definition.
('naive' can be similar in meaning to 'green')
'paper assimilated by church body' is the wordplay.
'paper' becomes 'i' (UK newspaper).
'assimilated by' means one lot of letters goes inside another.
'church body' becomes 'nave' (I've seen this in other clues).
'i' put within 'nave' is 'NAIVE'.
(Other definitions for naive that I've seen before include "Lacking wisdom and judgement" , "Too trusting and inexperienced" , "Unaffected or guileless" , "Ingenuous, easily deceived" , "Wet behind ears" .)