Hecho de cero:
Código PHP:
<html>
<head>
<script language="JavaScript">
var nColor = 0;
function changeColor(){
if (nColor == 0)
document.getElementById("blink").style.backgroundColor = "blue";
else
document.getElementById("blink").style.backgroundColor = "white";
nColor = (nColor == 0? 1: 0);
setTimeout("changeColor()", 500);
}
setTimeout("changeColor()", 500);
</script>
</head>
<body>
<table border="1">
<tr>
<td>
1
</td>
<td>
<div id="blink">
2
</div>
</td>
</tr>
<tr>
<td>
3
</td>
<td>
4
</td>
</tr>
</table>
</body>
</html>
Saludos.