Not exactly. In V1.000.111 they had completely alternate backgrounds for night and day. In the later version (I don't recall the exact number), they take advantage of the alternate background colour palettes that the SCI engine can cycle through (there are 4). So they switch to the night-time palette and then draw a unique night sky background made for each screen on top of the original background.
Interesting idea, actually. Despite how convoluted that sounds, it actually does save space because the backgrounds are created and saved as vector drawing "states" and not pixel-by-pixel like a regular bitmap. So instead of having large night-time alternates, they have smaller versions with the night sky only (half the size of the original background or less usually). I'm not sure how much more heap space that takes up during runtime, though. Must not be much, it runs fine.
Originally Posted by TomPravetz
This is the internet and you made a typo. Therefore, I won this argument. My opinion is now fact.