2 Backgrounds? Main and Content

Try this in the template_css.css line 1005:

#ja-mainbody #ja-content {
background:#000000;
float:right;
padding-right:2.5%;
width:70%;
}

Marked i red for the color.

The above is just for the content, if you want the whole white are to change(header,mainbody):
You can try to find the div called:


#ja-header, #ja-topstory, #ja-spotlight, #ja-container, #ja-footer {
background:#000000;
margin:0pt auto;
text-align:left;
width:750px;
}


There you can add the color you wanna have.
When that is done you might need to go trough the css file again to remove any unwanted colors showing up.