Puoi fare cosi.
Codice PHP:
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Exercise 1</title>
<script type ="text/javascript">
var coloreOriginale = null;
function changeColor() {
if (coloreOriginale == null) {
coloreOriginale = document.getElementById('box').style.backgroundColor;
}
if (document.getElementById('box').style.backgroundColor == coloreOriginale) {
document.getElementById('box').style.backgroundColor = "#299930";
} else {
document.getElementById('box').style.backgroundColor = coloreOriginale;
}
} // function changeColor()
</script>
<style>
#box {width: 100px;height: 100px;border: 2px solid red;}
</style>
</head>
<body>
<div id ="box" onclick ="changeColor();">Clicca qua</div>
</body>
</html>