[Rise]

без jquery

<select id="sel">
    <option value="0">zero</option>
    <option value="1">one</option>
    <option value="2">two</option>
    <option value="3">three</option>
</select>

<script>
document.getElementById("sel").onchange = function(){
    if (this.prev) this.prev.style.color = "black";
    this.prev = this.options[this.selectedIndex];
    this.prev.style.color = "red";
}
</script>