I'm really worried about the combination of the green color and the strange odor. I hope I'm being and alarmist in this case, but the first thing that came to mind was something my parents (both MDs) told us kids about. Those two symptoms together smack of a serious, rapidly progressive, potentially fatal disease called gas gangrene. Green skin and gas are the two classic symptoms of this particular type of gangrene (there's several kinds). If it is that, only immediate treatment can save the life of the person (or chicken) afflicted.
The odor is often like a combination of chlorine and rotting flesh (ugh!)Humans don't normally get it unless they have wounds that air can't get to and they don't get prompt treatment. It's done LOTS horrible death and damage in wars until recently for those reasons. Until they came up with penicillin, it always killed many, many wounded soldiers.
I didn't know if poultry got it so I did a quick Google and apparently they can and do get it, and the symptoms seem to exactly match what you described.
Here's a link to the first article I ran across:
http://www.zootecnicainternational....ntal-reproduction&catid=6:veterinary&Itemid=8. I'm sorry, but from what I could quickly scan, it appears to have a high mortality rate and (edited) recurrence if the conditions that caused the case aren't changed.
If it were me, I'd call a vet and/or take the dead chicken in immediately for a diagnosis and find out what treatment and/or management changes to use. From what my parents told me, if you've ever seen a gas gangrene case before, you'll recognize it instantly, so your vet may be able to tell immediately if that's what it is. Apparently if you catch it really fast, penicillin can stop it but chickens sometimes get it through their intestines, so it may not show symptoms fast enough for you to catch it easily.
Important note: If someone in your household is a diabetic, keep them well away from it! Diabetics can get it through even a small scratch on the skin and, because of poor blood flow, it can spread as fast as and inch and hour in a bad case.
Keeping my fingers crossed for you and your chickens! I'm sure hoping that it's not gas gangrene but from all the horror stories my parents told, I'd err on the side of caution on this one.
Please give us an update!
Ann