var color1="green";
var color2="red";
var color3="blue";
var color4="black";
var color5="yellow";

function flash()
{
 var crosstable=document.getElementById?document.getElementById("flashingborder"):document.all?document.all.flashingborder : ""
 if (crosstable)
 {
  if (crosstable.style.borderColor.indexOf(color3)!=-1)
  crosstable.style.borderColor=color2
  else 
     crosstable.style.borderColor=color3
   
 }
 
}

setInterval("flash()",300)
//-->