You know how I said that there was another gem like Amethyst. Well I'm pretty sure it's Onion. The titles of future episodes are:"Onion Friend and Old Friends". In Onion Friend Onion has an obsession with Amethyst and has been painting her for a long time. There is even a picture in the background that looks like it's Amethyst in the Kindergarten. In Old friend Steven helps Amethyst reconnect with an Old friend, I think the old friend is onion but in a different form/design. There may have even been foreshadowing in the sneak peek of "Onion friend" where Onion jumps out of the screen and he leaves a hexagon shaped hole. Amethyst's gem is a hexagon.

*this was made before "onion friend" so please don't comment with corrections.*