Screw back for black again, perhaps (6)
I believe the answer is:
redraw
'black again perhaps' is the definition.
I can't judge whether this definition defines the answer.
'screw back' is the wordplay.
'screw' becomes 'warder' ('screw' is an informal term for a prison warder).
'back' shows that the letters should be reversed in order.
'warder' written backwards gives 'REDRAW'.
'for' is the link.
Can you help me to learn more?
(Other definitions for redraw that I've seen before include "Pick over" , "Find a new winner" , "Sketch again" , "Warder (anag)" , "Delineate again" .)