Orbit is an excellent theme. You might find that if you navigate to Dashboard > Appearance > Orbit Options > CSS user, and then enter your style modifications in the CSS field and save the changes, that might do the trick.
Example: Enter #main-footer { background-color: #000000;}
and save the changes, and it should probably turn the footer background colour from green to black. Substituting your colour of preference for #000000, should do the trick.