Black Diamond takes White diamond's place.
How her powers work: she rips a gem's gemstone out and bubbles it. To prevent the gem from poofing, she uses a special type of bracelets, which:
Keeps a gem reformed without their gemstone,
Has them under her so called "control".
If the bracelets are removed, the gem's physical form vanishes like a cloud. Black isn't really controlling their minds: the Gems simply behave like her. The photo below is a perfect example how a controlled gem by black looks like.
Until Navy fusing with her significant other during Era 3 ball, Red Pearl wasn't under Black's control.
