Innocent when gallery is devoid of paintings (7)
I believe the answer is:
artless
'innocent' is the definition.
(I've seen this in another clue)
'gallery is devoid of paintings' is the wordplay.
'gallery' becomes 'art gallery' (synonyms).
'is devoid of paintings' becomes 'less' (I can't justify this - if you can you should give a lot more credence to this answer).
'art'+'less'='ARTLESS'
'when' is the link.
Can you help me to learn more?
(Other definitions for artless that I've seen before include "Without guile or affectation" , "Natural - uncontrived" , "Plain" , "Simple and natural in manner" , "Naive - unskilful" .)