A simple snippet I created to help out a Twitterer where the background color changes as you scroll down on the page:
<head>
<title>Change Color on Scroll</title>
<style>
body {
background-color: yellow;
transition: all 1s ease-in;
}
div {
min-height: 2000px;
}
.color {
background-color: red;
}
</style>
</head>
<body>
<div>
</div>
<script>
window.addEventListener("scroll", scrolling, false);
function scrolling(e) {
// change background color after scrolling 500 pixels
if (window.pageYOffset > 500) {
document.body.classList.add("color");
} else {
document.body.classList.remove("color");
}
}
</script>
</body>
Cheers,
Kirupa 
