> I have started to work on your scene, to adapt it even more.
> 
> Yes, you are right - changing the atmospheric colors does not lead to
> straight, expected results, but to unexpectable new colors. I believe
> (but I have no clue about media and density), that the reason for this
> color problem lays with the fact, that you specify the colors within the
> density map. I wonder, if there is a way to use neutral shades for the
> density map, and move the color map into the pigment statement right
> below the coordinates of the cloud layer.

Yes.
Some of the medias in your sample code have neutral colour_map.
If the media have a global colour, and a non-neutral colour_map, then 
the rgb values are multiplied together : media rgb<1, 0.5, 0.2> and 
colour_map entry rgb<0.3, 1, 0.1> give rgb<0.3, 0.5, 0.02>

It should be noted that with scattering and absorbing media, you get 
shadows. That imply some amount of self shadowing. If the media is not 
of a neutral tint, that mean that the remaining get illuminated by a 
tinted light of the complimentary colour.
A blue scattering or absorbing media's shadow will be yellow.
It can get really complicated when you have multiple scattering and 
absorbing medias as each one will cause some shadowing on all the others.
You don't want the container to have any colour as it will make it visible.


> I wonder, if I can use these two suns as light sources instead of a
> traditional light_source, when filling them with media?

Yes. Use looks_like as follow :
// Big red Sun
light_source{
  < 80.0, -0.0, 35.0 >*33.0 rgb<3,0,0.1>
  area_light 12*33*x 12*33*y 33 33 circular orient adaptive 0
  looks_like{
   sphere
   {
    < 0.0, 0.0, 0.0 > 1.0
    pigment
    {
     gradient y
     color_map
     {
      [ 0.00 rgb < 0.0, 0.0, 0.0 > ]
      [ 0.50 rgb < 0.0, 0.0, 0.0 > ]
      [ 1.00 rgb < 3.0, 0.0, 0.1 >*5.0 ]
     }
     translate < 0.0, -0.5, 0.0 >
     scale 2.0
    }
    finish { emission 1.0 }
    //scale 12.0
    //scale 33.0
// translate < 80.0, -0.0, 35.0 >*33.0
   }
}
// Small blue Sun
light_source{
  < 80.0, 12.0, 46.0 >*33.0 rgb< 0.1, 0.3, 20.0>/10
  area_light 33*x 33*y 33 33 circular orient adaptive 0
  looks_like{
   sphere
   {
    < 0.0, 0.0, 0.0 > 1.0
    pigment { color rgb < 0.1, 0.3, 20.0 >*10.0 }
    finish { emission 2.0 }
    //scale 33.0
    //translate < 80.0, 12.0, 46.0 >*33.0
   }
}

Remove the other light.
You now have two coloured shadows with fuzzy edged.
Adjust the brightness ot the lights as needed. The may be way to bright 
as they are now.

> 
> ------------------
> 
> 
> 
> ---

> http://www.avg.com
> 
Those anti-virus tags mean nothing as some virus imitate them.

When you have multiple medias:
Work on one untill it's correct.
Comment it out.
Work on the next one.
Repeat untill you have set all medias.
Activate two medias.
Tweak them a little if needed.
Add the others one by one making some small adjustments as needed.

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