The background for that part is coming from the main Body of the CSS on the homepage (line 154).
body {
background-color: #fff;
color: #333;
font-family: 'Open Sans', sans-serif;
font-size: 20px;
font-size: 2.0rem;
font-weight: 300;
line-height: 1.625;
margin: 0;
}
Since the widget area itself is shrunk in width/size, the background of the main body shows up.
If you wanted to make the front-page-2 widget area FULL WIDTH, it’s possible, just let me know. Here is sort of an example of what that would look like (it can be adjusted if needed) – http://demo.appfinite.net/elevate
I’m only mentioning the example if you only plan to have those 2 widget areas. It would make more sense to have it full width, unless you have other ideas/plans. Just let me know