I would guess that the black is part of ripening and they probably ripen fully to red. They remind me of some smaller peppers that I'm growing now, but mine are more of a Thai with a bit less heat.
I've never tried a pimenta before so I have nothing to compare it to but it sure looks a lot like Bhuter's pimenta leopards. I'll ask the guy who grew them to see if I can get any more info.