<link href="//netdna.bootstrapcdn.com/bootstrap/3.0.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//netdna.bootstrapcdn.com/bootstrap/3.0.0/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<!DOCTYPE HTML>
<html>
<head>
<style type="text/css">
body {
background-color: red;
transition: background-color 7s;
}
</style>
</head>
<body>
<script type="text/javascript">
var colors = ["#FF3547", "#ff1744", "#ffa726", "#eeff41", "#00C851", "#40c4ff", "#8c9eff", "violet"];
var i = 1;
window.setInterval(function(){
document.body.style.backgroundColor = colors[i];
i++;
if (i === colors.length){
i=0;
}
}, 5000);
</script>
</body>
</html>
