One of our cup manufacture customers got creative. Their factory was getting congested by an array of clear pneumatic tubing to the point where they could not visibly detect one cup line from the other. Their engineers wanted an easy way to distinguish the lines visibly and asked for colors. We obliged. The tubing pictured to the right was coated with a colorant that adheres (or rather embeds) to the tubing for a permanent colorant. It only embeds to the outside wall so it has no effect on the cup or any FDA or ESF compliance.