Yes, that makes sense. 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). FoW seems a good choice for that, yes. I still would leave the FoW color black, just add information to the light texture.
Where do materials emit light/brightness? I also wanted to implement an option for material light with different colors.

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.