2
you can use the feature of smarty templates to obtain this
for example i report here a part of code of the block of the newbb module "show recent discussion"
<{foreach item=topic from=$block.topics}>
<tr class="<{cycle values="even,odd"}>">
<td><a href="<{$xoops_url}>/modules/newbb/viewforum.php?forum=<{$topic.forum_id}>"><{$topic.forum_name}>a>td>
<td><a href="<{$xoops_url}>/modules/newbb/viewtopic.php?topic_id=<{$topic.id}>&forum=<{$topic.forum_id}>"><{$topic.title}>a>td>
<td align="center"><{$topic.replies}>td>
<td align="center"><{$topic.views}>td>
<td align="right"><{$topic.time}>td>
tr>
<{/foreach}>
then you need to define the classes
odd and
even of two different color in the css of your theme and you reach the result