How to change from the grey and white checkerboard background back to white?

I was working on a map with around twenty something layers. The different layers were all just paths with a white background and I was writing street names on them. While cut and pasting, I hit something on the keyboard that changed all the backgrounds of the layers to the grey and white checkerboard background (which might have something to do transparency, I'm not sure...). I'm not sure what I pressed and I'm trying to get the background back to white for all the layers instead of the checkerboard grey and white boxes. Any help would be greatly appreciated. Thanks!