var boje = ['red', 'green', 'blue', 'yellow', 'violet', 'pink', 'grey']; setInterval(function(){ document.body.bgColor = boje[ Math.floor(Math.random() * 6) ] }, 3000);
<h1>Jednostavna smena boja</h1>
body{ font-family:Arial; text-align:center; color:#fff; transition: all 0.3s linear 0s; text-shadow:1px 1px 10px rgba(0,0,0,.3); }