Twenty Eleven Background Color

I have created a child theme and revised the css to my liking but have one issue that has me stumped…

On this page (or any page where the ‘length’ or height of the content is less than the ‘length’ or height of the sidebar), the background color between the main area and the footer is same as for the ‘body’.

I do not see where I can assign a color to a style/element to fix this.

Any thoughts?