I think that's actually bruising. I've seen it before on birds (grew up with half our house being an aviary) who have had injuries. For example, if they whack the leg on something, or if it just gets hurt somehow, the whole limb can bruise bright green. It would also explain the limping. That looks more like a wound that has bruised, and some feathers have fallen out from the swelling (you can see it's swollen).
Edit: Here's some more info:
https://lafeber.com/vet/trauma/#:~:text=Bruises normally turn green in birds due to the presence of biliverdin.
Edit 2: And here's a pic from this very site:
Edit: Here's some more info:
https://lafeber.com/vet/trauma/#:~:text=Bruises normally turn green in birds due to the presence of biliverdin.
Edit 2: And here's a pic from this very site:
