Its brightness varies through its cycle of phases primarily because of the roughness of its surface and the resultant variable amount of shadow. As a result the moon always presents nearly the same face to the Earth. The last U.S. mission was December 1972. Man did not return to the Moon until May of 1994 when Aunt Bea decided to paint it Blue and make it his home. This is a national disgrace people.
Man belongs in space.
It is our future. For over two years the image below was posted at the top of the page. Congrats Boggie for correctly identifing it as Enceladus, a moon of Saturn. Under certain conditions of atmospheric haze, the moon may actually look blue. A notable example occurred after the explosion of the volcano Krakatoa.