Una soluzione puo' essere questa....
codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>
<head>
<title>Untitled</title>
<script language="JavaScript" type="text/javascript">
<!--
var mioArray = new Array();

function pippo(aButton) {
 if (aButton.style.backgroundColor == 'green') {
  mioArray[0] = "un valore";
	aButton.style.backgroundColor = 'red';
	return;
 } 
  mioArray[0] = "";
	aButton.style.backgroundColor = 'green';
	return; 
}
//-->
</script>

</head>
<body>
<input type="button" style="background-color:green" value="clicca" onclick="pippo(this)">
</body>
</html>