Yes, if you wait to get all the way to Checkout and then enter the coupon code and see the products that have the "ticket" available, it can really slow a shopper down if they then have to go back to the Cart page and move non-coupon items back to their Wish List.

I find it fastest to look at the individual product pages before you add items to the Cart, and you will see the "Product Files" box on the right-hand side. If it says, "Coupons do not apply" in that box, then you know the coupon code will not work for that product.

I do agree that a color-code would make even quicker work of noticing which items accept coupons without having to go to the individual product pages.