Try this:
.greenText{ background-color:green; }_x000D_
_x000D_
.blueText{ background-color:blue; }_x000D_
_x000D_
.redText{ background-color:red; }
_x000D_
<select_x000D_
onchange="this.className=this.options[this.selectedIndex].className"_x000D_
class="greenText">_x000D_
<option class="greenText" value="apple" >Apple</option>_x000D_
<option class="redText" value="banana" >Banana</option>_x000D_
<option class="blueText" value="grape" >Grape</option>_x000D_
</select>
_x000D_