Considerations: Iterating through an array of class names and adding them to the Post Class

do_color_classes.php

<?php
/************* ADDING CLASSES TO POST_CLASS **************/
// every post has a few uniquely colored elements, rather than rely on CSS nth-magic, and to keep things smooth
// and not conflict w/ trying to use jQuery nth-magic in tandem w/ the endless scroll,
// the option is to get the server to do the heavy lifting,
// ideally it would be nice to pass the array of classes to iterate thru into the filter,

/**
 *
 * @param $classes
 * @return array
 */
function do_color_classes( $classes ) {
    // globalizations
    global $wp_query;
    global $array_index;

    // define an array of class names to iterate over
	// $classes_array = array( 'yellow', 'red', 'blue' );
	/**
	 * Note:
	 * consider a filter on your array that will allow you to do more
	 * outside of this function. Although at some point you may as well
	 * just run the code here.
	 **/
	$classes_array = apply_filters( 'filter_color_classes', array( 'yellow', 'red', 'blue' ) );

    // get the post count
    $count = $wp_query->current_post;

    // set the array index value
    if ( $count == 0 )
        $array_index = 0;

    // compensate for it starting @ 0;
    $count = $count + 1;

    // pass the class in to match the index.
    $classes[] = $classes_array[$array_index];

    // check the modulus, divide the post count by the length of the array,
    // this'll reset the index counter, and keep iterating thru the $color_classes
    if ( $count % sizeof($classes_array) == 0 )
        // reset the index
        $array_index = 0;
    else
        // +1 to the index
        $array_index++;

    return $classes;
}

/**
 * Note:
 * post_class filter found - wp-includes/post-template.php line 296
 * This filter only has 2 possible parameters and neither are usable to
 * pass extra data.
 * 
 * function post_class( $class = '', $post_id = null ) { ... }
 **/
add_filter( 'post_class', 'do_color_classes' );