As far as I can see it's only on the one eye. I don't think it would even really show up in a picture though, because it pretty much just looks part of the brown in his eye (I think that's why I just noticed it today). I don't think it bothers him either. It's a ring that goes all the way around, and it's a bit lighter than the brown of his eye (but is brownish colored too). We go to the vet Sept. 3rd, so hopefully it's just normal!!! :?
If it's not bugging him and you have an appointment soon anyway, I would just wait until then. Be sure to mention it to your vet and have him take a look, otherwise he might miss it too. I really have no idea what it could be.