I found a bicentennial quarter that has rainbow looking marks on it. One larger one on the top and a small one on the bottom. Can anyone tell me what this is?
Sometimes, when coins are exposed to various chemicals and conditions, they are "toned", often times a rainbow-y colour. You'll see it a lot with silver coins, especially Morgan Dollars. Here's a thread with pictures of various toned coins: http://www.cointalk.com/t135678/
Some people would pay a premium for toned coins, but it depends on the condition, as well as the type of toning. Some coins are "artificially" toned. Could you post a picture of it?