Those are the things that I learned in digital haha. I mean, we have been told that in art school too but never really emphasized or "forced" since art is more into creativity and freedom.

But for a naturalistic approach, I've learned that the colors usually are saturated and higher contrast if it's closest to the foreground then it fades in the middle ground then very less in the background. Think of the furthest distance to have like a "fog" on top of it. I have observed in various illustrations and they're right, they usually do it hahah. I guess in traditional painting we often just make everything in detailed since we don't really pay attention to the blurriness cos we thought that's how our eyes see it but in reality our eyes really just works like a camera, it has focus as well. :D