Untitled

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html lang="en" dir="ltr">
<head>
	<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
	<title>test</title>
	<style type="text/css">html, body, #wrapper { height:100%; margin:0; padding:0; }</style>
	<script type="text/javascript">
	function changeColor() {
	    
	}

	function init() {
		var wrapper = document.getElementById('wrapper');
		var blackBtn = document.getElementById('setBlack');
		var grayBtn = document.getElementById('setGray');

		grayBtn.addEventListener('click', function() {
		    wrapper.style.backgroundColor = '#' + grayBtn.value;
		}, false);
	}

	window.addEventListener('load', init, false);
	</script>
</head>

<body>

	
    <div id="wrapper">
	<button id="setGray" value="333333">Set gray background</button>
    </div>

</body>
</html>