Most blue films, in the end, set dad off (7)
I believe the answer is:
saddest
'most blue' is the definition.
('sad' can be similar in meaning to 'blue')
'films in the end set dad off' is the wordplay.
'in the end' suggests the final letters.
'off' is an anagram indicator.
The last letter of 'films' is 's'.
'set'+'dad'='setdad'
'setdad' anagrammed gives 'addest'.
's'+'addest'='SADDEST'
(Other definitions for saddest that I've seen before include "Unhappiest" , "Most gloomy" , "Most blue" , "Most unhappy" , "Most doleful" .)