What does saturation in design refer to?

Saturation in design specifically relates to the intensity or purity of a color. When colors are described as being more saturated, they are more vibrant and bold, whereas less saturated colors appear more muted or washed out. Therefore, when considering the options provided, the relevance of the boldness of colors directly aligns with the concept of saturation.

In the context of the other possible answers, the arrangement of elements deals with layout and composition rather than color properties, while the proportion of light and dark colors pertains more to brightness and contrast rather than saturation itself. Lastly, spacing between elements refers to the physical distance or gaps separating design components, which is a different principle unrelated to color saturation. Thus, focusing on saturation emphasizes how vivid and dynamic the colors in a design are, which is accurately captured by the idea of their boldness.