PS image background setting question

[jorgemonkey]

I somehow set the background on all my images to black, instead of the gray. I can't figure out for the life of me A) How I did it, and B) how to turn it back.

The white part of the screen is the image canvas size. The black part is what you see when the image is shrunken down smaller than the image window.

Oh, I'm using CS2.