A simple color animation.
$(".block").toggle(function() {
    $(this).animate({ backgroundColor: "black" }, 1000);
},function() {
    $(this).animate({ backgroundColor: "#68BFEF" }, 500);
});
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" 
                    "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
  <script src="http://code.jquery.com/jquery-latest.js"></script>
  
  <script src="http://jqueryui.com/latest/ui/effects.core.js"></script>
  <script>
  $(document).ready(function(){
    $(".block").toggle(function() {
    $(this).animate({ backgroundColor: "black" }, 1000);
},function() {
    $(this).animate({ backgroundColor: "#68BFEF" }, 500);
});
  });
  </script>
  <style>
  .block { 
    color: white;
    background-color: #68BFEF;
    width: 150px; 
    height: 70px;
    margin: 10px; 
  }
  </style>
</head>
<body>
  <div class="block"> Click me</div>
</body>
</html>