Blue, before being incarcerated, on a feast (6)
I believe the answer is:
spread
'a feast' is the definition.
(I've seen this before)
'blue before being incarcerated' is the wordplay.
'blue' becomes 'sad' (similar in meaning).
'before' becomes 'pre'.
'being incarcerated' means one lot of letters goes inside another.
'sad' placed around 'pre' is 'SPREAD'.
'on' acts as a link.
(Other definitions for spread that I've seen before include "Distributed over" , "Sort of betting" , "Distribute or disperse widely" , "Scatter - padres (anag)" , "Extend - banquet" .)