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