Implemented "rings winter" effect on Saturn (don't know if this effect has some name, "rings winter" is my invention). It is a well known effect of winter hemisphere became blue as if receives a rings shadow. This is because there become too cold for a methane haze which makes Saturn look yellowish. The atmosphere became clear and cloudless and we see just a clear blue air, like on Uranus and Neptune.

Before:

After:

The system is completely integrated into engine. New variables were introduced for surface and cloud layers and for rings to control the effect, which are:
- integrated into planet scripts to use with catalog planets;
- procedurally generated for procedural gas giants and cold planets;
- integrated into the planet editor.