Database driven CSS using parse_request()

According to : https://josephscott.org/archives/2010/03/database-powered-css-in-wordpress-themes/ you can hook into the parse_request() function to get it to serve up a php file as CSS…. which would then allow you to pull CSS from a database. helpful as this is a common feature in theme options, except i can’t get it to work for anything.

i enqueue the pseudo script so that it shows up in the header

function kia_wp_head() {
  wp_enqueue_style('dynamic', get_bloginfo('stylesheet_directory') . '/admin/ . '?my-custom-content=css');
}
add_action('wp_print_styles', 'kia_wp_head');

and then my custom parse request, which i dont think ever gets called… or if it does isn’t adding changing any CSS:

function my_custom_wp_request( $wp ) {
    if( isset($_GET['my-custom-content']) && $_GET['my-custom-content'] == 'css'  ) {

        # get theme options
        header( 'Content-Type: text/css' ); ?>

body {
    background-color: <?php echo 'red'; ?>
}

<?php
        exit;
    }
}
add_action( 'parse_request', 'my_custom_wp_request' );

any insights will be much appreciated.