Function to generate a random class name for a post body (kinda stupid obvious, I suppose)

content.php

<article <?php post_class('clearfix ' . oneMenu_randomColor() ); ?>></article>

functions.php

function oneMenu_randomColor () {
    $colorList = array (
        'cyan',
        'orange',
        'yellow'
    );
    shuffle($colorList);
    return array_pop($colorList);
}