I agree with your premise, but without having more information, I don't exactly understand your story.
From my experience, it's not unusual for a new employee to take weeks and even months before getting NEAR to the level of productivity of their more experienced peers.
I also agree that having a sort of differential pay system for new hires could make sense, that is very uncommon. The usual, when hiring, is to allow for an unavoidable period of learning and adjustment, during which a new employee "loses" money for the company, to be hopefully made up for in the long term.
This isn't specific to minorities, but impostor syndrome is a very real thing in the software industry, and minorities tend to suffer more from it - https://en.wikipedia.org/wiki/Impostor_syndrome#Demographics