What color is night? This simple question leads to some deeper questions about color in filmmaking.
This is the sort of question that vexes film and TV people because we're torn between two things: the need to follow conventions, so that the audience can follow what's going on, and the desire to be original. Or, to put it another way, we're a bunch of insecure fashion victims who lack the courage of our own convictions.
To be fair, as the excellent and hilarious TV Tropes website puts it, conventions in filmmaking have a purpose, in the same way that traditional storytelling repeatedly turns up the same characters and situations. Traditionally, or at least for decades, movies have rendered night as blue. The prototypical example of this, if not quite the earliest, was the first Terminator film, and since then we've increasingly found movies turning blue and orange. Websites dedicated to identifying examples of this trend exist (such as this 2010 example).
Accusations of unconvincing self-tan aside, it's pretty easy to understand what's really going on here: human skin is, with famous variability, some sort of brown. Brown is arguably a desaturated orange, and our traditional sources of light – fire, incandescent light, and the sun at sunset – are also warm in hue. Assuming night is blue, or perhaps teal, we've then achieved production design that fulfils a design guideline familiar to any first-year art student, because the two key colors in the frame are opposite each other on a color wheel, 180 degrees separated by hue.
Now we know why Bumblebee is the key transformer in Transformers: they love him because he's yellow. When was the last time you saw a green robot in a Michael Bay film? Complainers such as the website above frequently cite color grading as the core evil, but of course there's far more to production design than that, and most of it isn't even technical. If you want the frame to look teal and orange, shoot teal and orange subjects.
This concept of color separation is basic because it's old, and it's therefore an idea that's probably not going anywhere, notwithstanding widespread accusations of excess. So what color is night really? Well, traditionally it's blue, possibly because moonlight is really just reflected sunlight, and bluer than most of the other sorts of light which exist at night. Shoot a sufficiently long exposure in moonlight, taking into account reciprocity failure if you're shooting film or noise if you're working electronically, and you will discover that it looks exactly like sunlight.
In a lot of situations in which humans operate after dark, it's lit by incandescent light, which is slightly orange, or sodium vapour light, which is extremely orange. Physiologically, the human eye is most sensitive in the green, so green objects tend to look brightest at night, although in very low light we see mainly in black and white. So, night is either blue, orange, green, or monochrome, or most accurately, in natural conditions, it's exactly the same color as daytime.
Case closed.