I have a tooth that is 2 or 3 shades darker than the rest of my teeth. I was told that maybe it's from trauma as a kid (maybe hit in a fight?) What can I do the whiten that tooth so it matches the rest of my teeth?

You can get it done professionally (ask your dentist) or do it yourself - you can buy a tooth-whitening kit from any major pharmacist.

I don't think there's a permanent solution except getting a cap (expensive) or a screw-in (state of the art, and VERY expensive).