Communist writer is correct (3-6)
I believe the answer is:
red-pencil
'is correct' is the definition.
(to red-pencil can mean to correct or revise)
'communist writer' is the wordplay.
'communist' becomes 'red' (red can informally mean communist).
'writer' becomes 'pencil' (something which writes).
'red'+'pencil'='RED-PENCIL'
(Other definitions for red-pencil that I've seen before include "(Implement used to) mark revisions in manuscript" , "Edit" .)