Aperture help needed! I'm still learning...

The best advice I could give you would be to to into the Color brick and sample the background color. Adjust the hue, saturation and luminance to match your background as close as you can. You may have to then paint the adjustment IN in order to not affect other areas of the photo. You may get closer still by next working with the curves and again painting the changes. You can probably get close enough I would think.