CS3 background color?

So usually, the "background" in my photoshop cs3 is gray. But as I was just iconing, I might have pressed some random keyboard short cut and it changed to black. To see what I mean:



But all that black isn't actually part of the file, because if I save what is there, it comes out as just 100x100



So I'm really not used to working with my photoshop with a black background, so does anyone know how to change it?

Thank you!