Composer meeting King George is appearing in green (9)
I believe the answer is:
verdigris
'green' is the definition.
(thesaurus)
'composer meeting king george is appearing' is the wordplay.
'composer' becomes 'verdi' (I've seen this before**).
'meeting' is a charade indicator (letters next to each other).
'king' becomes 'r' (r is abbreviation for rex).
'george' becomes 'g'.
'appearing' is an anagram indicator.
'r'+'g'+'is'='rgis'
'rgis' is an anagram of 'gris'.
'verdi'+'gris'='VERDIGRIS'
'in' is the link.
(Other definitions for verdigris that I've seen before include "Green deposit" , "oxidation" , "Patina on copper" , "Greenish-blue coat on copper" , "Greenish blue coating on copper" .)