I realize that I’m responding to an old thread. Thing is: the forum makes the threads a lot more accessible (it’s sometimes a little more difficult to see the date).
But the main reason I’m still responding is because I think that this topic could still be relevant for future users.
Changing the background
Right click in your diagram and find the “Presentation Options” section. A sub-menu will open and in there you’ll find “Background color…”. That should fix your problem.
Now… I’m using version 14.1 and you use version 13, but I think that this option has always been available in Visual Paradigm.