... I'm more concerned with Mars suddenly darkening ...
At this point, this is just straight up whining, sorry. A few complaints every once in a while here won't make Nitrolith return tanned Mars or give in to some here who are hoping for a pale Mars like the other demons. The only way is to go support them on Patreon and make requests as is your right since you're giving them money to make this game happen.
Just to get the record straight.
I don't like it either especially since it happened half-way into the story, almost like a bait 'n switch, but the game is good enough that I put up with it. It doesn't significantly dampen my enjoyment for now. I would feel the same way if Mars suddenly become so pale without explanation and was spouting shit like "let's colonize your ass with my cracker meat, Sera".
Nitrolith did try to explain it apparently whereas Mars is literally spraying his skin but he is actually super pale like the other demons. The thing is, this was apparently an offhand comment somewhere on Patreon, it hasn't been brought up or explained in the story where it would feel more natural.
I imagine Mars might shed the human disguise and probably the not-blackface with it to showcase some truly powerful BWC porn and we will finally get a noteworthy explanation in the game. (sarcasm if it wasn't clear)
In truth, this wouldn't matter too much only if the quality of the story and art remains the same (or improves). That's why the use of AI is concerning because there's very few who can use it well enough to produce high quality CGs. Not generic slop. I don't really care about the ethics of AI otherwise.
If the quality drops then minor flaws (like Mars' inconsistent colors) become major flaws, a lot harder to ignore especially with no justification for it in the story.
Mars is from a fantasy world too so blackface isn't really a conundrum within the story but the game is drawn by a real person in our world who is trying to justify it in a ham-fisted way and is clearly leaning into BBC porn (akshually white dude with blonde hair and blues eyes underneath) when it wasn't at first, it was just standard netori.
Players aren't stupid (and hopefully Nitrolith knows that even if their audience are mostly porn addicts) and they pick up on this even if unconsciously. This is where the ick factor comes from and why even if you go back a hundred pages you'll find someone expressing concern or complaining about it.