I've heard it can also be vitamin A deficiency or sometimes that they can do a lot of chewing and take the orange coating off their teeth (although I think that's probably not accurate). It is best to get bloodwork done. Several of us have a list of "normal" blood values for chins as we've had it done. HOwever, your vet should also be able to provide you with those. Even if nothing big is wrong, its never bad to have some bloodwork on file as a baseline in the event of problems down the road.
Back in NC again! (Army wife and proud!)
Chinnies: Maureen, Max, and Muad'Dib
Cats: Daphne (who says, I only play with mousie toys with a string tail and a bell.)
And introducing: Tasselhof and Kittira (Hubbie's childhood cats, who are 10 and 9 repectively)