Пупел,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
td:empty{
background-color: #FFFFFF;
}
td{
background-color: #FF0000;
}
</style>
</head>
<body>
<table border="1" id="row">
<tr>
<td width="20" height="20"></td>
<td width="20" height="20"></td>
<td width="20" height="20">2</td>
<td width="20" height="20"></td>
</tr>
</table>
</body>
</html>