Boxes {Pro} has 13 different wallpaper background images that you can choose from to style your page.
Here they are all laid out for your amusement on a Collage2 page from YourHead.
You can also pick a plain colour background. In the Wallpaper Styles palette, select "Wallpaper Off" and then use the colour picker to select you colour.
I have also added 2 "Custom" images which you can replace and save in the them using a utility like RWMultitool.
The images are in the Contents/Images folder. "Custom.png" is a 150x150 pixel image tile and Custom02.png is a 1500 x 1500 pixel file which you can edit to fill the entire page background.
