Photoshop problem..

This is more of a PS7 program problem than all else.. but through some odd chain of actions, I've changed my workspace background from the default grey to a random red shade that I'd rather not keep.

Any ideas on how to change/remove it? What happened originally was that I used flood-fill and accidentally clicked outside the image at the grey area. I've tried flood-filling it again, I've tried resetting the work palette, and I've tried restarting Photoshop, but the results are the same.

Has this ever happened? Is this reversible? Any help is greatly appreciated. =)