I have just been testing this in my Moodle 3.0 using the equivalent Essential Theme.
To get this to work you need to first add the class="table" to the table itself.
Next all you have to do is add to the <td> tag the following:
class="success" if you want a green background color
class="error" if you want a pink background color
Sadly it does not work here but it does in Essential theme for Moodle 3.0
Hope this helps?