EDIT

/**

 * Provides the image names which can be configured in the theme settings to all

 * theme setting functions.

 *

 * @return multitype:string

 *     the list of image names which can be configured in the theme settings

 */

function _zen_dataportal_imagenames() {

  static $image_list = array('banner', 'body_background', 'page_background');

  return $image_list;

}

  $form['zen_dataportal_colors'] = array(

          '#type' => 'fieldset',

          '#title' => t('Colors'),

          '#description' => t('Configure colors where.'),

          '#attributes' => array('class' => array('theme-settings-bottom')),

  );

  $form['zen_dataportal_colors']['site_name_color'] = array(

      '#type'          => 'textfield',

      '#title'         => t('Site name color'),

      '#default_value' => theme_get_setting('site_name_color'),

      '#description'   => t('Set the color of the site name which is shown in the header. Must be a css color value like: #000000'),

  );

  //

  // custom images for banner, body and page backgrounds

  //

  foreach(_zen_dataportal_imagenames() as $which_image) {

    $image_label = str_replace('_', ' ', $which_image);

    $form['zen_dataportal_' .  $which_image] = array(

        '#type' => 'fieldset',

        '#title' => ucfirst(t($image_label)) . ' ' . t('image settings'),

        '#description' => t('If toggled on, the following image will be displayed.'),

        '#attributes' => array('class' => array('theme-settings-bottom')),

      );

      $form['zen_dataportal_' .  $which_image]['default_' . $which_image] = array(

        '#type' => 'checkbox',

        '#title' => t('Use the default') . t($which_image),

        '#default_value' => theme_get_setting('default_' . $which_image),

        '#tree' => FALSE,

        '#description' => t('Check here if you want the theme to use the image supplied with it.')

      );

      $form['zen_dataportal_' .  $which_image]['settings'] = array(

        '#type' => 'container',

        '#states' => array(

          // Hide the logo settings when using the default logo.

          'invisible' => array(

            'input[name="default_' . $which_image . '"]' => array('checked' => TRUE),

          ),

      // If $path is a public:// URI, display the path relative to the files

      // directory; stream wrappers are not end-user friendly.

      $path = theme_get_setting($which_image . '_path');

      $image = '';

      if (file_uri_scheme($path) == 'public') {

        $url = file_create_url($path);

        $path = file_uri_target($path);

        $form['zen_dataportal_' .  $which_image]['settings'][$which_image . '_preview'] = array(

        	'#type' => 'item',

          '#title' => t('Preview'),

          '#markup' => '<div class="image-preview"><img src="' . $url . '"/></div>',

        );

      }

      $form['zen_dataportal_' .  $which_image]['settings'][$which_image . '_path'] = array(

        '#type' => 'textfield',

        '#title' => t('Path to custom') . ' ' . t($image_label),

        '#description' => t('The path to the file you would like to use as your') . ' ' . t($image_label),

        '#default_value' => $path,

      );

      $form['zen_dataportal_' .  $which_image]['settings'][$which_image . '_upload'] = array(

        '#type' => 'file',

        '#title' => t('Upload') . ' ' . t($image_label) . t(' image'),

        '#maxlength' => 40,

        '#description' => t("If you don't have direct file access to the server, use this field to upload your image.")

      );

  } // END of loop over image names

 * @param $form

 *   Nested array of form elements that comprise the form.

 * @param $form_state

 *   A keyed array containing the current state of the form.

  foreach(_zen_dataportal_imagenames() as $which_image) {

    // If the user uploaded a new image, save it to a permanent location

    // and use it in place of the default theme-provided file.

    if ($file = $values[$which_image . '_upload']) {

      unset($values[$which_image . '_upload']);

      $filename = file_unmanaged_copy($file->uri);

      $values['default_' .$which_image ] = 0;

      $values[$which_image . '_path'] = $filename;

      $values['toggle_' . $which_image] = 1;

    }

    if (!empty($values[$which_image . '_path'])) {

      $values[$which_image . '_path'] = _system_theme_settings_validate_path($values[$which_image . '_path']);

    }

  } // END of loop over image names

   * in modules/system/system.admin.inc

 *  @param $form

 *   Nested array of form elements that comprise the form.

 * @param $form_state

 *   A keyed array containing the current state of the form.

  foreach(_zen_dataportal_imagenames() as $which_image) {

    // Check for a new uploaded logo.

    $file = file_save_upload($which_image . '_upload', $validators);

    if (isset($file)) {

      // File upload was attempted.

      if ($file) {

        // Put the temporary file in form_values so we can save it on submit.

        $form_state['values'][$which_image . '_upload'] = $file;

      }

      else {

        // File upload failed.

        form_set_error($which_image . '_upload', t('The image could not be uploaded.'));

      }

  } // END of loop over image names