Blackened Feathers?

[Wolf]

True, those mite repellents are pure poison and if we had known that you were using one we would have told you so.
There is so much that goes into keeping these guys healthy, that at best all we can do is to give them a minimally acceptable level of care and with the way that things work to affect them, we are all going to make mistakes now and then.
It is difficult to answer questions here, partly because of this and partly because in most cases the original poster doesn't know how everything comes together to affect them and so they don't provide enough information. This in not really their fault, and I think at some point we have all done the same. It is difficult to know what to include when asking for answers to what is affecting our birds.

[Pajarita]

Well, although I would NOT use or recommend using any of these products (they are pretty useless as well as unnecessary with parrots and might be risky), I don't think the discoloration of his plumage came from them. These products are made of a substance similar to what the mothballs are made of and although they can cause cancer, liver and kidney damage, anemia, etc, this happens when the product is ingested and not by inhaling the gas (smell) they produce when exposed to air (inhaling A LOT would cause nausea, vomiting, etc). I would tend to think that something else caused the stress bars but, as long as he is getting healthy plumage now, it's fine.