What type of security feature on the PASS system logo changes color?

The correct answer is color shifting ink. This security feature is designed to enhance the accessibility and functionality of the PASS system logo by providing an easily recognizable color change when viewed from different angles or under varying lighting conditions. The color shifting effect not only adds a layer of security that is difficult to replicate but also helps individuals quickly identify legitimate documents.

This type of ink is often used in secure documents and identification cards to prevent counterfeiting, as it requires sophisticated printing technology and can be easily verified by the trained eye. Understanding how color shifting ink functions is crucial for recognizing authentic documentation within border security contexts, as it plays a significant role in the identification process and helps deter fraudulent activities.