Html Bottone che cambia colore

<style type="TEXT/CSS">
.bottone{BACKGROUND:red; FONT-WEIGHT: bold; FONT-FAMILY:Verdana}
</style>
<script language="JavaScript">
function on(colore) {
event.srcElement.style.backgroundColor=colore
}
</script>
<form>
<input class="bottone" onclick="window.open('http://www.fotopiufoto.blogspot.com','_self')" onmouseout="on('red')" onmouseover="on('yellow')" type="button" value="Prova" /></form>