I don’t think that’s how it’s being used in that quote. “I made her tan so I could see cute brown girls” doesn’t make sense if it’s being used an an honorific because, like you said, it has nothing to do with skin color. It’s like saying “I used -Sama so I could see cute brown girls.”
I see what you mean, like “I made Nagataro darker to see dark girls cosplay.” but you’d think for something that seems geared towards ab English speaking audience that they wouldn’t use “tan” without italicizing it or something so we know to read it as a loan word instead of what it we would normally see it as. Especially since both versions are coherent sentences, but one doesn’t make sense if you don’t know the honorifics or if they’re even using them.
Also, have literally no idea why I’m trying to “correct” what is likely a made up post 😂