I've been chasing that "lit from below" look with my clouds for some time now. The best way to achieve it with Vue seems to be using the "spherical" render mode where your world becomes a sphere (instead of an infinite flat plane). It makes for some incredible lighting options, but unfortunately everything seems to take 5 times as long to render. For this scene I've rendered the sky as a background first (as I did with "Skygate") and then worked on the foreground as I would in the normal "flat" Vue scene. It was a lot easier to do preview renders this way :-)