"Darker colors carry a lot more weight than lighter ones. Lightness and darkness are powerful tools for balancing designs."

It is uncertain why we see darker colors as heavier than lighter colors. According to research, an image is perceived as more “natural” when the darker shade is at the bottom. If the perceptual system prefers heavier objects at the bottom and lighter ones at the top, this shows that screen layout should mimic the physical environment where gravity pulls heavier objects to the bottom.