Enthusiastic study in painting (6)
I believe the answer is:
ardent
'enthusiastic' is the definition.
('ardent' can be similar in meaning to 'enthusiastic')
'study in painting' is the wordplay.
'study' becomes 'den' (I've seen this before).
'in' is an insertion indicator.
'painting' becomes 'art' (I've seen this before).
'den' inserted into 'art' is 'ARDENT'.
(Other definitions for ardent that I've seen before include "Very keen" , "Loving and fiery" , "full of zeal" , "'Fervent, impassioned (6)'" , "Ranted badly and became earnest in love" .)