Over time, as I've been developing all the other stuff, I think a fairly clear vision of the three particular aesthetics of the game have crystallized fairly well -
1 - Lunar city/other human structures
The city (which I still need to name) is built out of a mixture of local and imported materials, following the architecture of the turn-of-the-century inspiration - substantial amounts of brick and stone, large framing beams of iron and wood holding up the containment structure to keep the poisonous moon air out. Generally a warmer color palette, earthy materials, as well as greens and other colors from imported vegetation. I don't dare call it "steampunk" but there are similar elements in the palettes to be sure. In addition, the city has a canal system that links up with rivers outside, connected through large airlocks so lunar boaters can go in and out and cruise the rivers and seas at their leisure.
This is where I tentatively start in creating environment assets - I recently remembered that I have a copy of Aseprite, and with that I finally have returned to texturing for the game. It's been so long since I've done any texturing, and in this case, they're actual actual hand painted textures instead of just crushed photos like I was doing before.
Thusly, behold, texture #1, Grimy Block Wall 01 -

2 - Lunar wilderness
The moon itself is very different from the artificial structures built on it - strange vegetation and animals with an exotic color cast, and the earth in the sky peeking through the clouds in the thin atmosphere. The plants and trees are white-leaved with a multitude of colors of flowers and fruits popping out of them as strange vines curl and creep across the landscape. The landscape is jagged and harsh, although this doesn't deter the vegetation, which clings to whatever surface it can. There is substantial inspiration here from types of infrared film photography:
https://commons.wikimedia.org/wiki/File ... _Trees.jpg

https://commons.wikimedia.org/wiki/File ... _IR_M8.jpg

3 - Extradimensional domain of artistry and evil
... is a whole subject of its own. Another time...

I hope I am not causing annoyance with my repeated posts. I don't want to be spammy.