Is it possible to create a fill inside the pattern editing mode without having to put a shape behind it? I know there is the alternative method of adding a fill after you create the repeat tile in the appearance panel but sometimes I like to see what the background fill would look like while I'm in the middle of creating the repeat.
Note: The following was done using Illustrator CC, so hopefully this will still be valid in CS6. I don't have an old copy to check unfortunately.
There is a way to contrive this; it's a bit of a hack and it will require a little bit of setting up. It still involves putting a filled shape behind the artwork so I'm not entirely sure if it will suit all your requirements, but anyway here goes . . .
Make a rectangle the size of the artboard, and fill it with your desired background colour. Then lock the object in the layers panel.
Draw the objects you want for your pattern.
Do Window > New Window. This will open up a second view of your document in a new tab
Select the objects that make up your pattern, and do Object > Pattern > Make
Return to the first Tab, i.e. the original view, and edit your pattern there in that view. The filled rectangle background will be visible as you edit the pattern. Note that all objects will be visible in this view including any others on your artboard. I suppose you could temporarily hide them in the layers panel if they are getting in the way.
Here's the screenshot. The blue area shown here is the background rectangle.