Who is White Diamond's twin? Black Diamond?
Does this other Diamond have a Pearl? What does she look like?
Why did Black Spinel come to Homeworld?
Lol, its an old AU I made way before Future came out, but thanks for your interest!
Ive actually been working on re-designing the Black Court for a bit.
But to answer your questions:
Yup! In the AU, White and Black were twins born at the same time. They ruled Homeworld together but due to differences of opinion after making First Contact with other alien life, Black Diamond took her court and fled to the deeper parts of the Galaxy. White forbade the very mention of her name by that generation if gems, so by the time Yellow, Blue, and Pink came around there were no gems left that remembered Black.
Black went on to form a new society with the organic races she found, blending the then-fledgeling gems she had created and these organics into a new society and its own way of life.
Due to the difference in Society Structure, Pearls created in that Court function very differently being more akin to Team Management. Their ability to store and process not only items but vast quantities of information means most Pearls in this Court are often leading teams of other Gems typically in daily living like you would see in construction, business management, ect.
There are a couple different kinds of Pearls: Dusty, Black, Silver, and Golden. Their colour doesnt really effect what job they take due to Gems having less of a hierarchy structure under Black.
The gems most commonly seen in the "Assistant/GemSiri" role like Pearls are, are usually Tanzanites or Tourmalines but not always. Black Diamon's main assistant that would fit the closest role to The Pearls is actually a Selenite.
Black Spinel actually doesnt go to Homeworld, but goes to Earth following the events of the final episode (Pre-Future) after Steven sent out his message to the Universe and Black is curious to see what lead to White finally agreeing to change.
Don't think Black's Court is some utopia either. It has its own problems that spring up when you have one immortal race that is constantly intermixing with many different and flexible cultures and Black's desire for harmony was acrually the driving force behind the issue and how a desire for harmony to the point of erasing one's own culture and sense of self was actually one of the larger parts of the story.
Im chipping away at some new character references for the main new gems (Black Spinel, Black Diamond, Onyx, Selenite, Tanzanite, Dragon Fire Opal, Moss Agate, alongside a few fusion)