the engine seems not to expose the sky color to lua.
what i would like to do for modding/custom game is to change this color and - optionally - change size/positions/numbers of suns and moons.
i am not involved in the engine code that far that i could change the api yet, so maybe someone could think of me if he/she is coincidentally working somewhere in this area. ;)
edit: i fear this is hardcoded in the client part of minetest, so modding that may require extending the network protocol too. ugh!