<style type="text/css">
li a{ COLOR: #fff } 
.red{ BACKGROUND-COLOR: red } 
.blue{ BACKGROUND-COLOR: blue }
</style>

{dede:arclist typeid='1' titlelen='40' row='20' typeid="" }  
<li [field:global name=autoindex runphp="yes"](@me % 2 == 0)?@me="class='red'":@me="class='blue'";[/field:global]> 
<a href="[field:arcurl/]">[field:title/]</a>
</li>
{/dede:arclist}