How can I change a backround color inside article

I use a free version .
Can I change a backround color on my article ???

Hi there!
You have to edit the file style.css to change you background.
For example, there is a property:

#header {
	background:url(images/header.png) left top repeat-x;

or

body {
	background:url(images/top.jpg) 50% top no-repeat;

.
This is code of Metropress that I'm using for my site. But I think, it is similar for smthemes.