I'll make this simple and plain. A background dust cover is something every single three dimensional game has, without exception.

They are unreachable, and divide the player from the unknown in the distant.

The earliest of dust covers range to side scrollers for Sega, where the background looped as you progressed through levels, changing at the start of a new level.

In consoles such as the SNES, day to night transition was introduced, and two or more dust covers crossed the screen over time or player steps.

With the introduction of the Sony PlayStation, Y Gen games had more than ten dust covers on the background, and gave a new meaning to day to night transition.

Real time became a bigger theme in the gaming industry to add to realism, along with a game clock to mark day to night transitions, such as games like Bully, and Fable.

Next Gen games do as much as they can to beautify day to night transitions. Games like Grand Theft Auto: San Andreas use fifty multiple toned bars that cross the sky over the course of the day.

Now, games like Far Cry 2 dynamically decide the sky color, paying close attention to shadow, sky color, sun texture, clouds, even sun reflections.