Some sombre tones in French language (6)
I believe the answer is:
breton
'french language' is the definition.
(I've seen this before)
'some sombre tones in' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'BRETON' can be found hidden inside 'sombre tones in'.
(Other definitions for breton that I've seen before include "Inhabitant of NW France" , "Language of NW France" , "Frenchman" , "Cooked with cheese and/or breadcrumbs on top" , "Person from Brittany" .)