Как вариант...
<!DOCTYPE html>
<html>
<head>
<!--
<script src="http://code.jquery.com/jquery-latest.js"></script>
<link rel="stylesheet" type="text/css" href="tmp.css" />
-->
<style type="text/css">
.tr tr:first-child {
background-color: green;
}
.tr tr:last-child {
background-color: red;
}
</style>
<script type="text/javascript">
</script>
</head>
<body>
<table>
<tbody>
<tr>
<td>1</td><td></td><td></td>
</tr>
<tr>
<td>2</td><td></td><td></td>
</tr>
</tbody>
<tbody class='tr'>
<tr>
<td>3</td><td></td><td></td>
</tr>
<tr>
<td>4</td><td></td><td></td>
</tr>
<tr>
<td>5</td><td></td><td></td>
</tr>
<tr>
<td>6</td><td></td><td></td>
</tr>
</tbody>
<tbody>
<tr>
<td>7</td><td></td><td></td>
</tr>
</tbody>
</body>
</html>