ok not saying this is for sure it... But my cham ended up with black teeth and he was raised on the Earth pro products.... Sooooo it may very well be the beginning of staining to the teeth...I use Arcadia earth pro-A every day and then Repashy multivitamin every 2 weeks (just used it today).
I use a humidifier at night aimed in the enclosure, it ups the humidity to about 70% at night during the winter
I have talked to a handful of people where their chams teeth did the same thing. You can see his pearly blacks below. lol