I have 2 related (ish) ideas to improve the visual aspect of the mod.

First, there could be a version of true darkness that only affects subsurface levels. Maybe even the further down you go, to darker it gets. This would make lamps more important, and give a very different feel to lower surfaces. This should obviously be togglable for people who dont like true darkness. I have Dark Night installed, which does most of this, but the top surface also has true darkness.

Second, also to improve the visual aesthetic on subsurfaces, the layer of rock around the outside of the buildable area could extend further. Maybe it could fade out as it goes out further. This could mean instead of the void tiles, theres a specific rocky texture that goes there instead.