Why are objects that are about to "move" in a cartoon a different shade?

I’ve noticed over the years that when some object in a cartoon is going to move (a rock, wall panel, car door, etc. it is almost always a different shade of color that the other like objects around it are.
Why is it seemingly so difficult for the artists to make the object that’s about to move or be moved the exact same color as the rest of 'em?

Because they didn’t care enough? Because differnt artists illustrate the background and the moving parts? Because it is an artifact of the clear cell painting technique used in classic animation?

Again, because no one cared enough to devote that much attention to “continuity” for a one-reel filler entertainment?

Makes sense, I guess I’m not familiar with the stages that a cartoon goes through from start to viewing. You say that a part that is about to move can be drawn by a different artist using a different palette?
Here’s a follow up then. Why is the “part about to move” (henceforth called PATM) a different color sometimes several seconds (which I guess would be dozens of frames) before the part actually moves? Why not just one or two frames before- making it less noticeable?

It could also be because the non-mobile things are beneath several layers of cel, which could affect the color.

I can’t answer your question about timing, however.

They talk about this on one of the Simpsons’ commentaries. Supposedly even if you use the same color on the background and the cel, it comes out differently on camera. Possibly because the cel is raised above the background while being filmed? I’m not sure. They talk about how difficult it is to get the colors to match, and how much easier it is now that they use computer coloring.

It’s because the PATM isn’t part of the background scene. It’s on a separate layer of transparency that’s laid over the background–the cell DrFidelius referenced, if I recall the terminology correctly. The PATM isn’t necessarily a different color, but it looks different because it was on top of the transparency and all of the background objects were under it.

Making the PATM change just a frame or two before the movement would have required making at least two otherwise identical background images. Besides being more work, the artists could have accidentally introduced other discrepancies in the background at the transition. It would have been more hassle than it was worth.

In cel animation (which is rarely used these days) one team of illustrators would work on the still backgrounds, and another would work on the actual animation. Take a look at Scooby Doo. The backgrounds are vivid and colorfully painted, and the characters are one or two solid colors. Anything that’s going to move is going to be made completely by the animators, not the background artists.

The moving parts are made on cels, clear plastic sheets like you might see used on an overhead projector. If a character’s mouth is moving, but not their body, the body is drawn on a different cel, and the cels are placed on top of each other and photographed. The body cel stays in the shot for say, 5 frames, and the head cel is swapped out for each frame where it’s different.

This is all AFAIK and vague. I’m not an expert on animation. Nowadays nearly everything’s done on computers.

Have you seen this in recent cartoon? I only see this in really old, hand-painted stuff (e.g. Snow White, old Mickey Mouse cartoons).

Scooby, Flinstones, Jetsons etc, that era of cartoon. I think I’ve seen it on the Simpsons too.

To summarize what others have said, and perhaps expand on it:

  • backgrounds are created by one department. The animation cells (that’s celluloid film sheets) are drawn by one group of artists, inked by another, and colored by a third.

  • matching colors just in the animation cell is hideously difficult, especially when you consider how lighting changes affect the colors. Matching colors from cell to background when the two are created by different people, in different media, at different times (and the backgrounds may be recycled over and over) is nearly impossible. It could be done, but it would require a substantial investment in time, material, and manhours. This is not the sort of thing Hanna-Barbera was interested in doing.

  • technology has completely changed how classic character animation is done. I don’t think anyone works directly on celluloid anymore, unless they’re going for a specific look like the cartoons of the 30s-80s.

It’s incredibly prominent on the old Rocky & Bullwinkle cartoons. Anytime they show a close-up of Bullwinkle talking, his jaw (the only thing moving in the frame) will be a completely different color from the rest of his face.