In which aspect of art does "color value" primarily affect?

Color value primarily affects the emotional tone of a work by influencing how colors are perceived and experienced by the viewer. Within the realm of visual arts, color value refers to the lightness or darkness of a color, which can significantly alter the mood and feelings conveyed in an artwork. For example, lighter values tend to evoke feelings of happiness, openness, or serenity, while darker values may invoke a sense of sadness, mystery, or intensity.

Artists often manipulate color value to guide the viewer's emotional response and enhance the narrative of the piece. This use of color value can create depth, focus, and contrast, directing the viewer's attention and contributing to the overall atmosphere of the artwork.

In contrast, the other aspects mentioned in the question—composition, physical size, and subject matter—may be influenced by color, but they do not primarily hinge on the value of color itself in the same direct way that emotional tone does. Hence, the significance of color value lies in its ability to anchor and express feelings within the artwork.