Rodney Brooks of Wanaka asks :-

Why is the moon yellow at night but white during the day?

Kirsten Franklin, a physicist at Otago University, responded.

When you look at the sky during the day it looks blue, not black the way it does at night. This is because sunlight is scattered from the air above you, and mostly it is the blue end of the light spectrum that is scattered in a way that reaches your eyes. This gives distant objects, such as far-off mountains, a blue tinge, and makes the moon look more blue-white during the day.

At night, the moon often looks more brownish. This can be partly due to the light coming from the moon having the blue light scattered out of it, leaving it more red, like the colours of a sunset. The distance above the horizon matters too - a low "harvest moon" can look spectacularly orangey. It is also because the colour of the moon is on the whole rather like brown dirt! Due to the age of the close-up photos of the lunar surface, it can be hard to tell when NASA photos are in colour, but there are neat examples like photo AS11-37-5480 from the Apollo 11 section at http://www.apolloarchive.com/apollo_gallery.html.

The eye's receptors dont register colour so well under low illumination. Also, it is quite hard for our eyes and brains to pick the colour of an object at the best of times. It depends on what you expect, and what near-by things you are judging against. I like to compare it to trying to determine the colour of my fridge at night. I'm seeing a shade of grey, but I know my fridge is white, and so I have a very difficult time trying to decide, "What shade of grey is that?" I keep thinking it is "white in poor lighting". How you interpret the colours is influenced by what you expect.