Prova questa (da stato normale a fade):

Codice PHP:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Untitled Document</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<script type="text/JavaScript">
function setOpacity(el,value) { 
    el.style.opacity = value/10; 
    el.style.mozOpacity = value/10; 
    el.style.filter = 'alpha(opacity=' + value*10 + ')'; 
} 
function fade(el,stop){ 
    var opt= 10; 
   var timeoutID = window.setInterval(f, 100); 
    var self= el; 
    function f(){     
        if(opt>stop){ 
            opt--; 
            setOpacity(self,opt); 
        } 
        else { 
            window.clearTimeout(timeoutID); 
        } 
    } 
} 
</script>

</head>

<body>
<div id="myDiv" style="width:200px; height:200px; background-color:#0066FF" onClick="fade(this,'1')"></div>

</body>
</html>