Changing Margin Color

Hey, I’m kinda new to this, but how do I change the color of my blog margin without changing the color of the content section?

This is what I changed in the code in firebug-

body
{
	font-family: Verdana, Tahoma;
	font-size: 9px;
	background: #524b41 ;
         margin: 40px 95px 0px 95px;
}

However, that changes the color of the whole page, I would like to be able to keep the area around my posts white.

Also, while I’m asking questions, when I resize my window to 800×600 everything screws up. I assume I need to assigned a fixed width but I’m not sure where to do that either.

Thanks, James