<div id="sign">this is test!</div>

<style type="text/css">
.out{background-color: gray;}
.over{background-color: red;}
.down{background-color: yellow; }
</style>

$(function(){
var sign=document.getElementById("sign");
changBkColor(sign);
});
function changBkColor(obj){
obj.onmouseover=function(){ this.className="over"; };//鼠标悬停事件
obj.onmouseout=function(){ this.className="out"; };//鼠标离开事件
obj.onmousedown=function(){this.className="down";};//鼠标点击时触发事件
}

/* $(obj).hover(inFunction,outFunction)
*　等同于$(obj).mouseover().mouseout();
*/
$(function(){
$('#sign').hover(function() {
$('#sign').addClass('over');
}, function() {
$('#sign').removeClass('over').addClass('out');
});
});