function oddeven_post_class ( $classes ) {
global $current_class;
$classes[] = $current_class;
$current_class = ($current_class == 'odd') ? 'even' : 'odd';
return $classes;
}
add_filter ( 'post_class' , 'oddeven_post_class' );
global $current_class;
$current_class = 'odd';
/* Example CSS: */
.even {
background:#f0f8ff;
}
.odd {
background:#f4f4fb;
}