How can I disable the form confirmation message? I'm referring to the green box that informs the user that they have successfully submitted their form.
In particular, I'm wondering if I can remove it without writing any php. Is there anything in the admin interface?
There is no option in Drupal's core that gives you the ability to disable messages but there is a module for that: disable_messages.

Still, I like this approach, which uses drupal_get_messages function implemented in hook_form_alter:

/**
 * Implements hook_form_alter().
 */
function my_module_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  // Define the $form_id for the form which you want to suppress messages for.
  if ($form_id == 'hide_messages_form_id') {
    $form['actions']['submit']['#submit'][] = 'my_module_submit';
  }
}

/**
 * My custom submit handler.
 */
function my_module_submit($form, &amp;$form_state) {
  // Hide drupal 'status' messages. Equally use 'error', 'warning' or 'NULL'.
  drupal_get_messages('status');
  // Or display your own message.
  // drupal_set_message(t('My message.'));
}