Sun's appearance tab. Disc diameter 1. Corona size 0. Lighting of atmosphere tab. Even though the visible part of the sky is black, there is sufficient blue reflecting from the parts of the sky which are not visible in the image for the green showing through the snow to be visibly green, and for there to be a hint of blue in the shadowy parts of the clouds and in the shadows of the mountains at the edge of the lake.
Sliders are at the default levels.
Lock colour with atmospheric blue unchecked. Levels at the default settings. I had not changed the terrain in any way, so it was only necessary to save the world file and the atmosphere settings to be able to recreate this scene at a later date. Finally, to show you the special problems of a night snow scene, I have moved the moon out of the picture into the position occupied by the sun in the daylight version of this picture, so that the moonlight is coming in from due left, with the moon, now invisible, quite high in the sky. Although the sky and the water are still dark, most of the snow is now in direct moonlight instead of in shadow, and looks as though it is in daylight.