Try this once
var count=0;
var time;
var timer_is_on=0;
setTimeout("timedCount();", 3000);
function timedCount()
{
if(count == 6){
document.getElementById('blinkyellow').style.backgroundColor = "yellow";
}
count=count+1;
time=setTimeout("timedCount()",1000);
}
function doTimer()
{
if (!timer_is_on)
{
timer_is_on=1;
timedCount();
}
}
Also change the class on the td to an id like this
<table><tbody><tr><td id="blinkyellow">Col 1</td></tr></tbody></table>
Hope it will help you