At night, when the moon is right overhead, it looks white. White light is made up of all different colors of light, including blue. . . When the moon is right overhead, it comes straight through the atmosphere, so not much of the blue light gets scattered. But when the moon gets close to the horizon, it isn't coming at you straight on. It's kind of slanting at us, and it's going through a lot more air.. . The more air the white moonlight has to go through, the more chance for the short wavelength (blue) light to get scattered out. The green light is pretty short too, so it gets filtered out too. . . What's left is the red and yellow light. . . And that's why you only see the red and yellow light when the moon gets close to the horizon, and that's why the moon looks red oor yellow whenever it is about to rise or set.