When I copy and paste an image into Photoshop, it has a purple tint to it. When I user Save For Web, it previews fine. What default setting would affect the tint of the canvas?

what are you copying and pasting from?
Another guy on the board..i forget who had this same problem (purple tint) and none of us could figure it out.

I found this although i don't think it will fix your problem but you can try it.
http://www.graphic-design.com/Photoshop/Tips/gamma.html

so far this was the only thing I found that looked like a similar issue

Internet Explorer

I think a Windows Update messed up the driver for the monitor or something. My resolution was 1024 x 768, but it rebooted to 800 x 600.

For future reference, the solution to the purple tint was EDIT >> COLOR SETTINGS and choosing the correct setting beside RGB.

leave it to microsoft