I don't quite understand the need to mandate racial caricaturizations in every modes of communication. I would find it upsetting if every pieces of texts and quotes were prefaced with an "origin" indicator to aid forming prejudices. Why have it in manga?
If you are part of a marginalized group, it is both nice to the individual and productive for societal-level integration if you find yourself represented in media, especially if it's a generator with a promise of "generate anyone".
No one here is mandating shit, GP asked a friendly question in a most respectful manner, which prompted an informative answer from OP even. If such interaction generates such an allergic reaction in you, the problem is not with the grandparent comment.
I really think this integration predominantly means systemic internalization of racism, with side effect of affirmative actions. When ethnicity is expressed with intent, a distinction is made, and distinction is synonymous to discrimination. Or classification, for that matter.
What mandate? It's a product designed to be used by living, breathing people and people tend have various preferences. Do people requesting darker skinned models somehow upset you more than people who request red haired models?
Okay, I backtrack a bit, GP didn't specify that they want an adjustable ethnicity, only skin colors, and I made an assumption that exaggerated ethnic features is the intent.