What must the tattoo ink be in relation to the animal's skin color?

The requirement for the tattoo ink to be of a contrasting color to the animal's skin color is essential for visibility and identification purposes. A contrasting color ensures that the tattoo is easily distinguishable and can be read at a glance. This is particularly important in a veterinary setting where quick identification can be crucial for the animal's care or to verify ownership.

For instance, if an animal has dark skin or fur, using black ink would render the tattoo nearly invisible, making it ineffective. On the other hand, a light-colored ink applied to a dark surface enhances visibility, allowing anyone to read the tattoo without difficulty. Furthermore, a contrasting color helps to ensure that the tattoo remains legible over time, even as the animal ages or if there are changes in its fur or skin condition.

While transparency, water-based inks, or matching colors might seem like viable options, they would not achieve the necessary visibility for effective identification, which is why contrasting color is the optimal choice.