Lawyer backing green bill (6)
I believe the answer is:
advert
'bill' is the definition.
(I've seen this before)
'lawyer backing green' is the wordplay.
'lawyer' becomes 'da' (abbreviation for District Attorney).
'backing' says the letters should be written in reverse.
'green' becomes 'vert' (heraldic term for green).
'da' reversed gives 'ad'.
'ad'+'vert'='ADVERT'
(Other definitions for advert that I've seen before include "Publicity item" , "piece of publicity" , "Refer to the red vat" , "Commercial notice" , "Make reference or call attention to" .)