I must have mentioned this a dozen times but this happens because traditionally cuck porn tends to have race play in it. Subconsciously, Nitro seems to be going for that skin contrast, though he refutes it.
Nitro has personally said that he uses the "same colors" in every scene so Mars isn't actually changing skin colors, but if you take out photoshop and actually check the damn thing, yes. Mars does become much darker with pale women. It's very jarring and often hilarious to see Mars go from Tyrone to Drake to even Chad.
As for the proportions, most of it is because Nitro's art is evolving and what he finds sexy is also changing. He did say he started tihs game to practice drawing and he has much improved. He also gave himself the in-story excuse of the curse to change characters' bodies. However the art can get fucky especially in sex scenes. Mars' penis seems disembodied in some of the scenes, like the penis is attached to something other than his crotch. Cecille seems to lack half her bones, especially her clavicle and ribs in the side-to-side laying down position. Hands are pretty bad especially when he draws them held together. I can't even mention the new gyaru girl's animated scenes. Nitro does not do anatomy well. IIRC he said in the discord, not verbatim, that "anime art style allows you to get away with bad anatomy". This is true to some extent, but Nitro abuses it a tad much.
But most of this is for the trained eye. It does look sexy at first glance.