Transition

HTML

<div>

</div>

CSS

div
{
  width:100px;
  height:100px;
  background-color:red;
  transition: background-color 1s ease;
  -webkit-transition: background-color 1s ease;
}
div.green
{
  background-color:green;
}

JavaScript

window.setInterval(function()
{
	$('div').toggleClass('green');
}, 1000);