function neuro_add_css() {
$options = get_option('neuro');
$color = $options[('ne_color')];
$tdurl = get_template_directory_uri();


    if ( $color == 'grey'){

    echo '<link rel="stylesheet" href="$tdurl/library/css/grey.css" type="text/css" />';
    }

}
add_action( 'wp_head', 'neuro_add_css');