Final answer:
When a color is very pure and intense, it appears to be closer to the viewer in a painting due to the saturation of the color. Saturated colors create the illusion of depth and make the subject matter appear more advanced towards the viewer.
Step-by-step explanation:
An artist can indeed use color to indicate depth in a painting. When a color is very pure and intense, then it seems to be closer. This is partly because more intense, or saturated colors appear to advance toward the viewer, while less intense or muted colors seem to recede. Saturation refers to the intensity of color, and a color is considered to be fully saturated when it is in its purest, most authentic form. The primary colors, which are red, blue, and yellow, are examples of fully saturated colors at their purest form. In the context of color theory and art, as saturation decreases, the appearance of the color can start to look washed out, especially when white or black is added, leading to a diminished sense of depth. Therefore, by using highly saturated colors in certain areas of a painting, an artist can create the illusion of those areas being closer to the viewer compared to areas with less saturated colors.