Here's a little dose of color theory: the darker it is, the cooler everything looks, and the less contrast it has.
Whenever I have to do a series of images in photoshop, I create a palette layer, and include all the colors I use. This means everything can have perfect continuity, within a single image, and from one frame to the next in sequential art. To make a night scene as believable as possible, you must do the same thing to each color. This is incredibly easy on the computer.
With your palette on its own layer, do a color overlay. Use a very cool, almost grey blue.
Shoot for something like this:
Make adjustments as necessary, but this will make for a good, dramatic difference. Then, when you pick up the colors from your palette, it will find the adjusted colors. Paint away, and it will automatically look like cool, evening light! Here's the difference:
Illustrated Rachel - Daytime
Illustrated Rachel - Illuminated by Computer
I did cheat a little when it came to the hair color. The highlights were much lighter than I thought they should be, for only having light on a little bit of her hair. This is where one must use a discerning eye and take liberties!


