Herald compiler on ship turning green! (9)
I believe the answer is:
messenger
'herald' is the definition.
(thesaurus)
'compiler on ship turning green' is the wordplay.
'compiler' becomes 'me' (the person who is writing these clues).
'on' is an insertion indicator (as in clothing \'on\' a person).
'ship' becomes 'ss'.
'turning' indicates anagramming the letters.
'green' anagrammed gives 'enger'.
'ss' placed within 'enger' is 'ssenger'.
'me'+'ssenger'='MESSENGER'
(Other definitions for messenger that I've seen before include "Bringer of news, etc" , "One doing errands" , "Person carrying information to another" , "Communication carrier" , "Emissary, courier" .)