It's too wide a swath to be there b/c of,say, a shirt collar, and, besides, who wears just a shirt collar? A shirt collar is attached to a shirt which covers the chest which, in this case, is far darker than the neck? Could this photo be a ham-handed photoshop?
Meanwhile, Barack Obama's tan lines didn't get much attention. People should realize that his beach frolic this summer was to work on his tan.