I was trying to randomly put something together and came out with this interesting background.

1. Hit "D" to reset colors.

2. Filter>Render>Clouds

3. Filter>Pixelate>Mosaic - Cell Size: 17

4. Filter>Stylize>Find Edges

5. Filter>Stylize>Emboss - Settings: Leave at Default

6. Hit Ctrl + U to change the colors.