It's just nice to experiment, and get to know the capabilities of TG. And not everybody has access to all software, so if one gets something working within TG it may be handy for some users.
I added some nodes, but the black is still there. Just forget about this, I'd say. And also, I have wondered about (and mentioned) world scale opacity in pops one or two times in the last few years, but don't think it works as expected/needed (but haven't tried for a long time). It would be handy to make forest edges (on flat country) to have grazing edges (lowest branches eaten off), for instance.