http://www.anapsid.org/sight.html

Here is one peice of decent information. The sources look like they are credible from other studys. When I did my research on this I found a more indepth study log.. stating pretty much the same thing, the colors they do see are not robust, they are more in shades/hues.

I hope this helps you guys. but I really wish I could find that other study log, Im fairly certain it was from a university that had a herpetology department and they went into detail about how little color most snakes see. but I do remember it stating there are certain species that have superb vision and can see a broader color spectrum then others.