A really cheap way to have colored backgrounds without spending a wad of money for colored backdrops is to gel your background lights.
These gels are actually sheets of colored acetate, or whatever it's called, and they go in front of your flash. Mine are the ones that come with the holders for my flash. Other ones can be just the piece of plastic that are either taped or attached by velcro in the flash.
They can also color correct the flash in certain situations. Some photographers put green gels in their flashes when they shoot in flourescent lighting. As flourescent lights give out a green tint.
I mainly use the gels for effects or background colors.