Does it affect the value? Yes and no. Yes, it will be rejected by TPGers and yes it destroys any numismatic value, but an eagle doesn't have much to begin with. A nicely applied colorization may add value if you are selling to private individuals. Of course, like what other posters have said, they aren't equal, some are terrible others are quite nice. Just be picky and look for a good deal and you'll get a quality coin.