Fixative used in perfume has a light colour: French grey (9)
I believe the answer is:
ambergris
'fixative' is the definition.
(thesaurus)
'colour french grey' is the wordplay.
'colour' becomes 'amber' (amber is a kind of colour).
'french grey' becomes 'gris' (I can't justify this - if you can you should believe this answer much more).
'amber'+'gris'='AMBERGRIS'
'used in perfume has a light' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for ambergris that I've seen before include "Substance from whales used in perfumes" , "Perfume ingredient from whales" , "Sperm whale product used in perfumery" , "substance floating in sea" , "Sperm whale secretion used in perfume manufacture" .)