The Black Potaras are a set of ear rings wished for using the Dragon Balls after Evil Vegito's set was destroyed by Ukele when he tried to fuse with Gogeta.
The Black Potaras function exactly like a normal set of Potara ear rings, but they allow the users to de-fuse on command. They also appear black with yellow-ish bottoms and are shinnier than regular ones.
Gogeta and Evil Vegito used these to form Gogito while fighting against Buu (Final Form).