How can I see my website like a color blind person?

This website seems to do what you need.

If you don't want to depend on a web service, Chrometric is a free AIR-based browser that lets you toggle between different forms of color blindness. It also has the advantage of working in a live browser (such as WebKit), rather than for single URLs at a time.

There's also a colorblindness simulator add-on for Firefox.