modifying the default theme – weird background ?

On this page: DSA blog, I am trying to get rid of that light grey background around the blog. I need it to be the same color grey as the rest of the background. I cannot get it to happen.

I have changed the CSS. I have changed the images for the footer and the file that looks like it is causing that grey (file called kubrickbgwide.jpg). But it will not change.

Could someone please tell me where I am going wrong? What am I overlooking that causes that background? I know this is newbie question and appreciate your frustration but I would appreciate your help even more.