Green is unsmoked bacon. Prefer smoked myself. From a proper butcher. None of this plastic wrapped stuff which seems to be mostly water...dry cured is best.
If you're seeking really good bacon, this place supplies online. A friend of mine bought me some Black Bacon, which is sweet-cured with beer, from their shop recently. It wasn't cheap but it was gorgeous!
http://www.emmettsham.co.uk/
As others have indicated, the OED gives one definition of 'green' as "not dried, seasoned, smoked or tanned".