Nice to hear an update on the baby. I post every now and then, but mostly I just read. Just wanted to pass along that my second child had teeth issues. When her teeth started coming in, I noticed discoloration as well. For some reason, the tooth enamel did not form properly in utero. There is a name for it--maybe enamel hypoplasia? Anyway, this resulted in a lot of dental work on her baby teeth. However, her permanent teeth came in just fine. It might be worthwhile to ask your dentist. They might be able to tell from looking at it what it is.
Good luck. Keep giving your baby lots of love. That's what matters most. You are a good mom :)