change-acf-colour-picker-defaults.php

function my_acf_admin_head() {
  echo "<script>
  (function($){
    acf.add_action('ready append', function() {
      acf.get_fields({ type : 'color_picker'}).each(function() {
        $(this).iris({
          palettes: ['#111111', '#333333', '#555555', '#777777', '#999999', '#cccccc'],
          change: function(event, ui) {
            $(this).parents('.wp-picker-container').find('.wp-color-result').css('background-color', ui.color.toString());
          }
        });
      });
    });
  })(jQuery);
</script>";
}

add_action( 'acf/input/admin_head', 'my_acf_admin_head' );