this seemed like the best place to get an answer.

In some 2D animation, the "active" objects - those that move during the scene, or will be interacted with somehow - have a distinct style compared to background objects.

Is that a style choice or is there some technical or pragmatic reason for that (maybe it's faster to make or render?). I also find it curious that this happens across products and studios, pretty much in the same way - the "active" objects have distinct lines and brighter colors, while the background is somewhat amorphous in comparison.

Here is an example of what I mean, from Avatar: Legend of Korra:
[![enter image description here](https://i.stack.imgur.com/B4ogc.png)](https://i.stack.imgur.com/B4ogc.png)

Thanks!