To create a subdued feeling along with a sense of seriousness in her painting, Elizabeth will likely be changing the intensity of the colors.
Intensity refers to the brightness or saturation of a color. By using colors that are less saturated (more muted or desaturated), she can achieve a more subdued look. Additionally, she might also consider adjusting the value, which refers to the lightness or darkness of a color, to further enhance the serious tone of the painting.
So, while both intensity and value can contribute to the overall effect, the primary focus for a subdued and serious feeling would be on intensity.