On reflection finish with When The Saints or the blues? (7)
I believe the answer is:
sadness
'the blues?' is the definition.
(thesaurus)
'on reflection finish with when the saints' is the wordplay.
'on reflection' is a reversal indicator.
'finish' becomes 'end' ('end' can be a synonym of 'finish'**).
'with' says to put letters next to each other.
'when' becomes 'as'.
'the saints' becomes 'ss'.
'end'+'as'='endas'
'endas' backwards is 'sadne'.
'sadne'+'ss'='SADNESS'
'or' acts as a link.
(Other definitions for sadness that I've seen before include "distress" , "regret" , "Dolour" , "Misery" , "Emotion experienced when unhappy" .)