Changing site background color does not change triptych-wrapper background

Changing the Main Background color in Home » Administration » Appearance » Settings » Appearance only changes the color down to the bottom of the main-wrapper div. The background color of the div triptych-wrapper below it does not change, resulting in an odd appearance (doesn't match the preview image in Appearance >> Settings.) There does not seem to be any option on that settings panel to change the bg color for that section of the page.