function altrows(firstcolor,secondcolor)
{
var tableElements = document.getElementsByTagName("table") ;
for(var j = 0; j < tableElements.length; j++)
{
var table = tableElements[j] ;
var rows = table.getElementsByTagName("tr") ;
for(var i = 0; i <= rows.length; i++)
{
if(i%2==0){
rows[i].style.backgroundColor = firstcolor ;
}
else{
rows[i].style.backgroundColor = secondcolor ;
}
}
}
}