Which principle does not rely on color alone for accessibility?

The principle that does not rely on color alone for accessibility is Perceivable. This principle ensures that information and user interface components must be presented to users in ways they can perceive. It encompasses not just color, but also the use of text, images, sounds, and tactile feedback, allowing users to access content through multiple sensory channels.

For instance, text cannot only be distinguished using color; it should also have sufficient contrast, and information should be conveyed through patterns, shapes, or visible cues. By employing various modalities, we can cater to users with different needs, including those with visual impairments who may not rely on color perception.

The other principles, such as Operable, Robust, and Active, focus more on aspects like user interactions, compatibility with current and future technologies, and ensuring users can navigate and control the interface effectively. These do not specifically address how information is presented in a way that ensures it's accessible regardless of a user's ability to perceive color.