its a general vibe really. I've been in the nsfw sphere for a lot longer than most gposers, I know dogwhistles of problematic fetishization. I know what fetish mining looks like. They're skills I've picked up from being a swer for damn near a decade, though it doesn't make me an expert. I'm not really the authority on racial fetishization, I am just loud about it and bright skinned so people get comfortable asking me. Talk to poc in the community, get their opinions and value theirs' above mine. Personally, I side-eye stuff like this:
-blank-slate dark skinned chars. no customization, no funny lil personality quirks. just default spawned npc. its not an oc to them.
-dark skinned chars are never the focus of the pic. its always the light skinned one. never a shared spotlight (beyond tits/dick/coochie of the darker oc). pics will be framed in such a way to minimize the amount of space the darker oc takes up.
-read the captions. a lot of time how people talk, even without outright saying some fucked up shit, will give off rancid vibes.