Twitter Bootstrap - Full width background (image)

I'm currenly on a project and I'm trying out the awesome Twitter Bootrtrap including the responsive grid. All works fine and dandy except for one issue.

How do you give the .container (which holds the grid) a background color? Example:

<div class="container green">
    <div class="row">
        <div class="span6">
            <p>This is a test</p>
        </div>
    </div>
    <div class="row">
        <div class="span6">
            <p>This is a test</p>
        </div>
    </div>
</div>

.green{
 background:green;
}

When I add a color to the container it will turn green but leaves a margin on the left side, about 20px. How do I implement a full-width background?