Which aspect determines the visual impact of a color due to its brightness or dullness?

Saturation refers to the intensity or purity of a color. It describes how vivid or muted a color appears, which directly impacts its visual impact. A color with high saturation is bright and bold, while a color with low saturation appears more washed-out or dull. This concept is crucial in design because varying saturation levels can evoke different emotional responses and create different visual hierarchies within a composition. Designers often manipulate saturation to create focal points or to create a sense of depth and atmosphere in their designs.

In the context of the other options:

• Value deals with the lightness or darkness of a color, which affects the perception of brightness but not the vividness associated with saturation.

• Contrast refers to the difference between two or more elements, particularly in terms of brightness or color, but it is not confined to the quality of the color itself.

• Temperature relates to the warmth or coolness of a color but does not address vibrancy or dullness directly.

Thus, saturation is the most appropriate term that addresses the brightness or dullness of color.