functions.php How to add css/js depending on Template Name?

You can use wp_enqueue_style() before running get_header() in your blue.php file.

If you’re looking for a way to do that inside your functions.php file, then the init hook is a bit too early for is_page_template(). Try the wp_enqueue_scripts hook instead:

add_action( 'wp_enqueue_scripts', 'load_my_theme_files' );
function load_my_theme_files() {
    if ( is_page_template( 'blue.php' ) ) {
        wp_enqueue_style( ... );
    }
}

Hope that helps!