If the coin has been painted it is considered damaged by coin collectors. As it is now it is just a memento of the millennium. It still has its silver value and is worth at least what an ounce of silver is selling for on the day it is sold. Colored as well as gold plated coins make an interesting gift but have no collector value. The only way to get a value is to put it on a on line auction or see what someone would offer. I saw a colored set of state quarters, well up to the last one in a nice wood frame and it was impressive and would make a good item to pass down in the family but it has little collector value at least yet. Maybe in 100 years who knows. I would just keep it for now.