<?php
$the_query = new WP_Query(array(
    'post_type'     => 'post',
    'post_status'   => 'publish',
    'meta_key'      => 'colors',
));


$results = [];
while ( $the_query->have_posts() ) {

    $the_query->the_post();
    $credits = get_field('colors');

    if( !empty($color) ) {

        foreach( $colors as $color ) {
           $results [$color][]=array(
               'title' => get_the_title(),
               'link' => get_attachment_link(),
               'img' => get_field('photo')
           );
       }
    }
}

foreach ($results as $color => $posts) {

   echo '<div><h2>'.$color.'</h2>';

    foreach($posts as $post) {
        echo '<div><a href="'.$post['link'].'">'.$post['title'].'</a><img src="'.$post['img']['url'].'"></div>';
    }

   echo '</div>';
}

wp_reset_postdata();?>