What principle of design involves a gradual change from one feature of the design to another?

The principle of design that involves a gradual change from one feature to another is called "gradation." This principle creates visual interest and depth by transitioning smoothly between elements, such as color, size, or shape. Gradation helps to guide the viewer's eye through the design and can evoke a sense of harmony or movement. It is often used in both two-dimensional and three-dimensional design contexts.