Why Hollywood Darkness Persists in Film
This persists in modern films, even in scenes actually shot at night, for a simple reason: the cameras. To get good images, cameras need good light exposure; only specialized cameras can shoot worth a damn in the dark, and even then with quality below that of movie-quality. Despite what some people tend to think, one cannot simply "turn up the sensitivity" on film or digital cameras, as film will result in incredibly distracting, obscuring film grain, and digital sensors will have blotchy, color-fringed visual noise.
The easiest solution is to simply use a lot of stage lights to bring the scene to a reasonable level of brightness and underexpose from there; blue is used since that's the tinge of a moonlit nightnote , and therefore feels the most "natural".
