I am in no way an expert, since I myself have been doing this stuff for just over a month, but I'll try to help.
First of all, judging by how many femboy and futa images I have to scroll through while browsing Civitai galleries of other, unrelated tags, you might have found yourself a popular niche there. Just need to either shrink the dick and muscles for femboy connoisseurs or add big ol' tiddies for futa aficionados
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Jokes aside, could you post what prompts you were using (both positive and negative)?
The prompts the creator of the game himself is using for Tara (dark-skinned girl) are something like this:
28 year old athletic girl with tan skin, gorgeous, medium large breasts, thick body, long curly pink hair, green eyes, thick waist, (long hair:1.2), (brown skin:1.2), (athletic:1.2), slightly muscular
or
28 year old girl, gorgeous, medium breasts, thick body, long curly pink hair, green eyes
This is based on these (and other) pictures in his profile:
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So by remixing these images you should get her close to the original. It might require several attempts.
Mix-ups, like the one you experienced, happen on occasion. The AI on Civitai sometimes just mixes up prompts/traits/features of characters. If you pay close attention (I don't know why tf you would do that, instead of focusing on Laura getting railed, but still), you can notice, that in my pictures involving Nathan (has brown hair), AI was also making both Laura's and MC's hair brown(ish), despite my directions. In my experience it happens way less often with a male-female pair than with pairs of the same gender. I actually gave up on trying to create images with Laura and Tara together because it just kept mixing their features: making them both dark-skinned, giving them the same hair style/color, etc. As far as I can tell, there is no foolproof way to avoid it in Civitai. You just have to get lucky. Your best bet would be to use a local client like A1111 or ComfyUI, that has feautes to more clearly separate characters and their traits.
But male-female should still be fine most of the time. If you want to have Laura with a black man, I suggest using her normal prompts (1girl, 28 year old girl, cute, freckles, medium round breasts, short wavy black hair, black hair, ponytail, brown eyes, (red hair tie:0.5)) and using "1 african american man" for the man or simply using a more general "interracial" prompt. For a scene with Tara you could specify "1 caucasian man" to get the interracial scene. Though I am fairly certain that Civitai makes people caucasian by default, without specific directions. You can also give specific prompts more weight if AI keeps ignoring them. ((1 african american man:1.0)) (or 0.9, or 1.5) should tell AI that this feature is especially important for you. Bigger number — higher priority, though I rarely need to use anything more than 1.0.
Lastly, about pupils. My guess: it's a "feature" — the details are lost with distance. The AI just doesn't really know how to maintain detailed eyes, when it's not dealing with close up shots. In my experience, when trying to do full body shots and thus increasing the distance (or using side view/back view angles, the results are even worse. It might also just be that "MC's" (we don't actually have canonical MC appearance) face is in the shadow and he has brown eyes by default. So darker, similar colors just sorta blend together. You could add one of the detailed eyes LoRA's to improve the results:
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Alternatively, in order to avoid eye issue entirely (and reduce the chance of feature mix-up), you could just not show a man's face at all by using something like "face out of frame" prompt. 90% of the time it works every time.