Bootstrap 3: Missing gutters

Bootstrap 3 switched to using padding for the gutters rather than margins. So, the content is parted, but the boxes aren't. And a background-color will fill the padding as well.

Though, you should be able to get the desired effect by setting the background on inner boxes:

<div class="row">
    <div class="col-sm-4">
        <div class="box1">
            <h1>Test</h1>
        </div>
    </div>
    <div class="col-sm-8">
        <div class="box2">
            <h1>Test2</h1>
        </div>
    </div>
</div>

http://jsfiddle.net/PFxUk/

---

Though, the goal is just to apply the background to a single, wrapping child. So, if the headers definitely won't have any siblings, then you can possibly forgo the additional <div>s:

<div class="row">
    <div class="col-sm-4">
        <h1 class="box1">Test</h1>
    </div>
    <div class="col-sm-8">
        <h1 class="box2">Test2</h1>
    </div>
</div>

http://jsfiddle.net/G2gbG/