There have been many articles published by the NWTF on this subject.

Although you cannot ever rule out people interbreeding domestic turkeys with a wild bird and the like, there is a well documented and genetically proven color phase of the wild turkey. It's called the 'smoke' phase. Seen much more frequently in the southern states and pockets out west, it is definately there.

http://www.pgc.state.pa.us/pgc/cwp/v...a=466&q=152421

An article from the PA Game Commission including an excerpt about the color phases.

Article on NWTF website. Look under the 'Feathers' heading.