msdropdown: styling certain options differently from the others?

Question

I am creating the msdropdown from HTML, that is my code is like:

<select id="ex">
<option value="...">...</option>
..etc
</select>
..
$("#ex").msDropdown();

I want to have some of the options styled differently from the others (different background color and font color), and for that I tried changing the class of the options I want styled differently, that is, <option class="something".. > but msdropdown doesn't "take" this class when it creates its own elements. (I also tried <option data-className="... > but that doesn't seem to do the trick either)