Green iridescent feathers? Silver laced wyandotte.
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Alot of black birds will get the beetle sheen, do you have a "girl" that your questioning? If so if you have some pictures we can help you out :3
Are they all the same breed? Does the one in question have a redder comb, wattles, face? Does it have sharper neck feathers or tail feathers?
Ahh here is one :3 Yeah, I'd probably say cockerel, thats pretty red in the face and not much full feathering ^^