Your perception of an object’s color is affected by both its lighting and its surroundings. The first card you see in this exhibit is actually black—but it’s brightly lit. When it’s the only card in the light, it may look gray or even white. But as you raise lighter cards, each new card looks white and the previous cards look darker by comparison.
Our moon is also a brightly lit dark object—it’s dark gray, but in the spotlight of the Sun, it looks white. This photograph of the moon’s surface shows how dark it really is. Photo courtesy of NASA.gov.
(click image to enlarge)