Reserve of dye most supply (7)
I believe the answer is:
modesty
'reserve' is the definition.
('modesty' can be a synonym of 'reserve')
'dye most supply' is the wordplay.
'supply' indicates anagramming the letters (supply of letters to make).
'dye'+'most'='dyemost'
'dyemost' is an anagram of 'MODESTY'.
'of' acts as a link.
(Other definitions for modesty that I've seen before include "Humility; decency" , "Reserve" , "Unassumingness" , "Unassuming quality" , "Unpretentious style" .)