Вот, хоть немного по-приличнее...
<!DOCTYPE html>
<html>
<head>
<!--
<script src='http://code.jquery.com/jquery-latest.js'></script>
<link rel='stylesheet type=text/css href=tmp.css' />
-->
<style type='text/css'>
.logo {
color: green;
}
.logo1 {
color: blue;
}
.logo2 {
color: red;
}
.logo3 {
color: silver;
}
</style>
<script type='text/javascript'>
</script>
</head>
<body>
<div id="logo" class="logo">
<div id='sprite-hours'>
<div id='sprite-minutes'>
<div id='sprite-seconds'>logo</div>
</div>
</div>
</div>
<script type="text/javascript" language="Javascript">
var day = new Date();
var hour = day.getHours();
var o=document.getElementById("logo");
if (hour>=7 && hour<10) {
o.className = "logo";
} else if (hour<15) {
o.className = "logo1";
} else if (hour<18) {
o.className = "logo2";
} else if (hour<21) {
o.className = "logo3";
};
</script>
</body>
</html>