Top shade of nail polish remover (7)
I believe the answer is:
acetone
'nail polish remover' is the definition.
(I've seen this in another clue)
'top shade' is the wordplay.
'top' becomes 'ace'.
'shade' becomes 'tone' (synonyms).
'ace'+'tone'='ACETONE'
'of' acts as a link.
(Other definitions for acetone that I've seen before include "Industrial solvent" , "Remover of nail polish" , "Volatile stuff" , "Inflammable liquid" , "Paint thinner" .)