I have a tiny brown spot on one of my teeth? HELP?!?

I have braces, and it's on the tooth right of my front tooth. I noticed it two days ago.. I brushed and scrubbed at it, and some went away. So it can't be rotting? Or a cavity? WHAT IS IT? I'm scared that it will be there forever. I really want my teeth to be pretty... So, what is it? Any ideas?? Can my orthodontist remove it or my dentist? HELP.