Following code is used to change a page color from your select option in select box.
Copy and Paste following code in a simple HTML page.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Change Your page Background Color Using Java Script</title>
<script type="text/javascript">
function changeTheme(selColor) {
alert(selColor);
document.body.style.backgroundColor = selColor;
}
</script>
</head>
<body>
<h1>Please Select Your Page Background Color..</h1>
<select name="changescheme" id="changescheme" onChange="javascript:changeTheme(this.value)">
<option value="white">White</option>
<option value="red">Red</option>
<option value="blue">Blue</option>
<option value="orange">Orange</option>
<option value="black">Black</option>
</select>
</body>
</html>