Alternate border colors for Posts in WordPress

functions.php

//* Add even/odd post class for Posts in Posts page, Archives and Search results
add_filter( 'post_class', 'sk_even_odd_post_class' );
function sk_even_odd_post_class( $classes ) {

	global $wp_query;

	if ( is_home() || is_archive() || is_search() ) {
		$classes[] = ($wp_query->current_post % 2 == 0) ? 'odd' : 'even';
	}

	return $classes;

}

style.css

.odd.entry {
	border: 5px solid #288eb0;
}

.even.entry {
	border: 5px solid #eeac18;
}