Day for Night

Jay Holben has a nice article at DV.com on how to use natural lighting and your camera's white balance to achieve a nighttime look while shooting during the day:

That in mind, I decided to challenge myself to create a “night” look utilizing natural daylight — shooting day-for-night — without any augmentation with artificial lighting.
A day-for-night effect is, generally, achieved through gross underexposure. You’re rendering your highlights down to below middle gray and plunging your shadows into the abyssal blackness. Day for night works best when the natural light is backlighting the subjects and when you can keep the sky and the ground out of the shot — two things that will give away the cheat very quickly.

And here's an article on why night is usually colored blue in the movies, from The Academia Dictionary via io9. 

The Purkinje effect (sometimes called the Purkinje shift, or dark adaptation and named after the Czech anatomist Jan Evangelista Purkyně) is the tendency for the peak sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels.
This effect introduces a difference in color contrast under different levels of illumination. For instance, in bright sunlight, geranium flowers appear bright red against the dull green of their leaves, but in the same scene viewed at dusk, the contrast is reversed, with the petals appearing a dull red and the leaves appearing bright green.