Code to answer question on my blog: https://www.damiencarbery.com/2018/07/add-info-to-woocommerce-order-emails/#comment-8852

custom-variation-note-to-order-email.php

<?php
/*
Plugin Name: Custom note to order email (for variation)
Plugin URI: https://www.damiencarbery.com/
Description: Add a note to the order email if the order contains products with a specific variation name.
Author: Damien Carbery
Version: 0.1
*/

/* Add note about electronic licenses to the order email. */
add_action( 'woocommerce_email_order_details', 'dcwd_electronic_license_info_to_order_email', 5, 4 ); 
function dcwd_electronic_license_info_to_order_email( $order, $sent_to_admin, $plain_text, $email ) {
	// Only customers need to know about the delivery times.
	if ( $sent_to_admin ) {
		return;
	}

	$variation_name = 'White';
	$order_has_specified_variation = false;

	$items = $order->get_items();
	foreach ( $items as $item_id => $item ) {
		$product = $item->get_product();
		if ( $product->is_type( 'variation' ) ) {			
			$variation_suffix = ' ' . $variation_name;
			$variation_strlen = strlen( $variation_suffix );
			if ( $variation_suffix == substr( $product->get_name(), -1 * $variation_strlen, $variation_strlen ) ) {
				$order_has_specified_variation = true;
			}
		}
	}
	
	if ( $order_has_specified_variation ) {
		if ( $plain_text ) {
			echo "\nNOTE: This order has a product with the specified variation.\n";
		}
		else {
			echo '<p><strong>Note</strong>: This order has a product with the specified variation.</p>';
		}
	}
}