Mounted blue frames for one French artist (5)
I believe the answer is:
degas
'french artist' is the definition.
(I've seen this before)
'mounted blue frames for one' is the wordplay.
'mounted' shows that the letters should be reversed in order.
'blue' becomes 'sad' ('sad' can be similar in meaning to 'blue').
'frames' indicates putting letters inside.
'for one' becomes 'eg' (I've seen this in other clues).
'sad' back-to-front is 'das'.
'das' placed around 'eg' is 'DEGAS'.
(Other definitions for degas that I've seen before include "He produced works of art" , "Edgar -, Fr. artist" , "Edgar ---, ballet-dancer painter" , "He painted dancers" , "Edgar ---, Fr. impressionist" .)