function twentyfifteen_custom_header_setup() {
  $color_scheme       = twentyfifteen_get_color_scheme();
  $default_text_color = trim( $color_scheme[4], '#' );

  add_theme_support(
    'custom-header',
    
/**
 * Filters Twenty Fifteen custom-header support arguments.
 *
 * @since Twenty Fifteen 1.0
 *
 * @param array $args {
 *     An array of custom-header support arguments.
 *
 *     @type string $default_text_color Default color of the header text.
 *     @type int    $width              Width in pixels of the custom header image. Default 954.
 *     @type int    $height             Height in pixels of the custom header image. Default 1300.
 *     @type string $wp-head-callback   Callback function used to styles the header image and text
 *                                      displayed on the blog.
 * }
 */
    apply_filters(
      'twentyfifteen_custom_header_args',
      array(
        'default-text-color' => $default_text_color,
        'width'              => 954,
        'height'             => 1300,
        'wp-head-callback'   => 'twentyfifteen_header_style',
      )
    )
  );
}