> So the sun just makes everything bright, and nothing else (a sun of different color, along with the global "ambient light" would make the whole thing needlessly complex)

The way the "sun" works at the moment is basically just be letting sky material emit white color. The same mechanism could easily be adapted for other materials to emit light, such as lava emitting some orange-ish, or crystals some blue/white-ish color. That's why I referred to it as ambient light, not as sun... maybe we could call this something like "material lights"?

> Edit: One additional thing: The color value of that global light influences the brightness of the sun light at the moment. Otherwise, a dark red global light is not possible at the moment, because it gets normalized by the shader. The darker color is achieved by reducing the brightness of the sun.

As I said, I would prefer to keep these two concepts separate. By default the "sun" should make everything bright, and if a scenario author wants dark red light also overground, they should call SetAmbientBrightness() themselves. Sorry I didn't yet get to look at the details of your implementation, so this is my slightly uninformed opinion ;)