Yeah, so there have been many threads about this, most of which say that Tobi's identity will be revealed when he uses his MS.
Check out the last slide on this picture. What do you think? Bad scan or a hint from Kishimoto? In every other picture he has been shown with a normal SG eye, except in this one it clearly shows which MS he has.
Discuss and Enjoy.
This is his original one that I am referring too.