Beatty film (4)
I believe the answer is:
'beatty film' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for reds that I've seen before include "Left-wingers" , "Colourful communists" , "Scarlet and crimson, say" , "Scarlet communists" , "First snooker balls to be potted" .)