<html>
<head>
<script>
function tim(){
var elem=document.getElementById('flash');
var date=new Date()
var hours=date.getSeconds()
if(hours>6&&hours<19){
elem.className='morning'
}
else
if(hours>=19&&hours<37){
elem.className='day'
}
else
if(hours>=38&hours<48){
elem.className='evering'
}
else{
elem.className='night'
}
};
window.onload=function(){setInterval(tim,1000)}
</script>
<style>
.morning {color:green;}
.day {color:red;}
.evering {color:blue;}
.night {color:black;}
</style>
</head>
<body style="background:white;">
<div id='flash'>color</div>
<div style="color:red;">tratata</div>
</body>
</html>