I see people say Stealth blacks ability was so Sanji could be invisible cause judge didn’t wanna look at him, the raid suits existed long before current generation of Germa and before Sanji was born.
There’s a TV show about them that aired when Law (26) was a child and I doubt it was about a bunch of 2 year olds fighting...
Anyways the genetic abilities always seem to compliment the main ability. I have the feeling it would be an incapability of perception. Think Kuroko of Kurokos Basketball. Sanji was seemingly supposed to be the assassin of the group (judge probably trained him in swords for that reason) and invisibility only goes so far if you can’t be silent and imperceptible at the same time.
Diable Jambe doesn’t seem to be his genetic thing because he learned it through friction and still uses friction to activate it.
So if I were to put money on a mutation that he would’ve gotten it’d be the incapability to be perceived through haki