Green as everything in Jersey, say (6)
I believe the answer is:
callow
'green' is the definition.
(I've seen this before)
'everything in jersey say' is the wordplay.
'everything' becomes 'all' (all things).
'in' is an insertion indicator.
'jersey say' becomes 'cow' (Jersey is a breed of cow).
'all' inserted into 'cow' is 'CALLOW'.
'as' acts as a link.
(Other definitions for callow that I've seen before include "Green" , "23 [BRIGHTONIAN] actor" , "Immature and inexperienced, like youth" , "Jejune" , "Inexperienced or innocent" .)