Use a "contextual class" to color the panel green.
<div class="panel @(13)">
<div class="panel-heading">My Header</div>
<div class="panel-body">Hello World</div>
<div class="panel-footer">My Footer</div>
</div>
<div class="panel panel-success">
<div class="panel-heading">My Header</div>
<div class="panel-body">Hello World</div>
<div class="panel-footer">My Footer</div>
</div>