POV-Ray offers a variety of atmospheric effects, i. e. features that affect the background of the scene or the air by which everything is surrounded.
It is easy to assign a simple color or a complex color pattern to a virtual sky sphere. You can create anything from a cloud free, blue summer sky to a stormy, heavy clouded sky. Even starfields can easily be created.
You can use different kinds of fog to create foggy scenes. Multiple fog layers of different colors can add an eerie touch to your scene.
A much more realistic effect can be created by using an atmosphere, a constant fog that interacts with the light coming from light sources. Beams of light become visible and objects will cast shadows into the fog.
Last but not least you can add a rainbow to your scene.