Your writer writes in crimson — not green (7)
I believe the answer is:
ripened
'green' is the definition.
Both the answer and definition are adjectives. Perhaps they are linked in a way I don't understand?
'your writer writes in crimson' is the wordplay.
I cannot really understand how this works, but
'writer' could be 'ed' (I've seen this in other clues) and 'ed' is found in the answer.
The remaining letters 'ripen' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'not' is the link.
Can you help me to learn more?
(Other definitions for ripened that I've seen before include "(Of fruit) matured" , "Became mature" , "Matured, aged" .)