a:link,a:visited{text-decoration:none;}
        a:hover{text-decoration:underline;}
    

Method 1
        
for loop and arry for the colors
--------------------------------
window.onload=function()
{
    var oBtn = document.getElementsByTagName('input');
    var oBd = document.getElementById('db');
    var oVal=['green','blue','yellow'];

    for(var i=0; i<oBtn.length;i++) 
    { 
        oBtn[i].index=i; 
        oBtn[i].onclick=function() 
        { oBd.style.background=oVal[this.index];} 
    } 
}

Method 2
Creat two CSS files with different body{background: } settings. IF we need to change more than one color combinations, such as title,background,text,etc.This method is better.

<link id="l1" rel="stylesheet" type="text/css" href="css1.css">
<script>
function skin1()
{
    var oL=document.getElementById('l1');
    oL.href='css1.css';
}
</script>