esempio funzionante:
codice:
<html>

	<head>
	<style type="text/css">
	.spento{
		color:#A0A0A4
		}
	.acceso{color:#0000FF}
	</style>
		<script type="text/javascript" language="JavaScript1.2">
function Classe()
{
var pul = document.getElementById("pulsante");
pul.className="acceso";
}
	</script>
		<link href="stile.css" type="text/css" rel="stylesheet">
	</head>

	<body bgcolor="#ffffff">
	<form name="form1" method="post" action="">
	  <input name="Submit" type="button" class="spento" id="pulsante" onclick="Classe()" value="Invia">
    </form>
	

</p>
	</body>

</html>