Multigraph 3.2 was released today. It includes a new <background> tag that allows you use an arbitrary background color and/or image. It's documented in the new online user guide here, and there's a new online example showing it in use.
Note: this web site is for the old, Flash-based, version of Multigraph. Starting in December 2012,
from the site multigraph.github.io. Future projects