@Ceciliabr

I think I prefer dark level 2. The difference might seem minimal on these small pictures, but will probably be a lot more visible on a larger image.

By default, the dark value is 0.
You can test the minimum night brightness (dark value 1/255) with the beta version of the plug-in .
[If it's possible, I'll try to embed a dark level test instead of changing the value in the source code.]

On the two lower images I can see there is a blue hue that is more visible on dark level 1 than on dark level 2, but it seems to be the other way around on the two bathroom images. Does this have anything to do with sky texture or colour?

As the SimpleRoom.sh3d project has an outside opening, I used a black texture for the sky.