To apply a background color, just add the color name in a class element.
<div class="card-panel blue lighten-1">
<div class="center-align"> www.freetimelearing.com </div>
</div>
To apply a text color, just add -text
.
<div class="card-panel">
<div class="blue-text text-darken center-align"> www.freetimelearing.com </div>
</div>