If you ever look in your mouth and are able to SEE any color other then the white of your teeth you need to get it looked at.
It may just be stain or last nights dinner but it could be a sign of something much more.
When a dentist looks at your teeth he/she uses color change as one of the indicators to take a closer look at any particular area.
The pictures below are a case that we did just this morning.
The patient came in with a little darkened area on one of his molars.
After we got done getting out all of the decay out he was as close as you would ever want to come to getting a root canal. Once the decay gets down into the tooth you are no longer able to get to it with your toothbrush, floss or mouthwash. The bacteria simply set up shop in your tooth and start to multiply. Not Good.