To change the background of your pause menu pick up a shirt.
Go to the bottom right space of your item inventory. (not the letter inventory)
Press down to find a hidden inventory space and place the shirt in it.
Suddenly the shirt will become a new background for your pause menu and a "big dot shirt" (the old background)will appear in your inventory. To get your shirt back simply replace it with a different one.
The only down side is that you can't use your own patterns that you've made.
