Undressed gold turned neutral (2,7)
I believe the answer is:
au naturel
'undressed' is the definition.
(I've seen this before)
'gold turned neutral' is the wordplay.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'turned' indicates anagramming the letters.
'neutral' with letters rearranged gives 'naturel'.
'au'+'naturel'='AU NATUREL'
(Other definitions for au naturel that I've seen before include "Naked in French, to aural tune" , "Cooked plainly or raw" , "Very simply" , "Nancy's naked" , "Cooked plainly - naked" .)