system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do the moving parts of cartoons have a slightly different color? Like if a car for is about to open, it will be a slightly different shade of color until it opens. Then when it's closed/done moving independently, its color matches the rest of the car.
gpt
Those are animation cels. Rather than have the animator draw the background for each frame, they instead have one background sheet, and then a series of celluloid sheets with the movements of foreground objects.

Because of the different techniques for creating celluloid sheets, colour matching between the background and foreground was not perfect. This is why you can tell when something is going to be a moving object based on its colours.