Hard-core red, maybe wearing sheep's clothing? (4-2-3-4)
I believe the answer is:
dyed-in-the-wool
'hard-core red maybe' is the definition.
(a committed communist)
'wearing sheep's clothing?' is the wordplay.
I cannot really see how this works, but
'wearing' could be 'in' (you are 'in' the clothes you're wearing) and 'in' is present in the answer.
'sheep's clothing?' could be 'wool' (I've seen this in another clue) and 'wool' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for dyed-in-the-wool that I've seen before include "Fixed in one's opinions or attitudes" , "Retain" , "Of firmly fixed opinions" , "Fixed and uncompromising" , "Unchanging in a particular belief" .)