When presenting data in a table, vBulletin will usually alternate the background color of cells to assist in readability.
The background colors used for these two alternating cells are controlled by the First and Second Alternating Color classes.

Example of element using these classes:
<table class="tborder" cellspacing="1" cellpadding="6">
<tr>
<td class="alt1">Tag using the First Alt. Color class</td>
<td class="alt2">Tag using the Second Alt. Color class</td>
</tr>
</table>
