My dentist told me that I could have a tooth colored filling. I believe they're more expensive than dark colored silver-mercury fillings and do they work?

Yes, tooth colored filling materials have been around for quite some time now. In some cases, the investment for tooth colored restorations can exceed that of the old silver, mercury filled material and there's a good reason for that. Tooth colored (composite) fillings require more attention to detail and more time for actual placement. The materials used in composite restorations are more costly as well. And yes, tooth colored fillings do work! Composite fillings bond directly to the tooth and are light cured, making the tooth stronger than it would be with a silver filling. They bond and strengthen the teeth, whereas the silver mercury fillings fill the holes, but do not strengthen the tooth.