Which of the following characteristics is not part of the functionality design principles?

The characteristic that is not part of the functionality design principles is contrast. Functionality design principles primarily focus on how a system operates and interacts with users, emphasizing aspects such as flexibility (the ability to adapt to various situations), accessibility (ensuring users can access and utilize the software or service without barriers), and robustness (the ability to handle errors and unexpected situations gracefully).

Contrast, on the other hand, is more related to visual design and the effectiveness of communication through graphical elements. While contrast plays a crucial role in user interface design by enhancing readability and visual differentiation, it does not directly pertain to the underlying functionality or operational principles of a system. Thus, it is not classified as a functionality design principle.