What about the blue background as you can see it in this image?
Both, seasons and day/night times will need an huge amount of additional graphics. Not only that's a lot of work, but also it would be too much graphics to be loaded all at the same time. That's why we changed season for the whole game in the past. It may be possible to reload specific graphics when needed, but that may take some seconds, so we shouldn't to it too often. Finally, we don't know yet how we handle seasons, but it's much more likely that we will add them than the idea with day/night.