Hmm, don't remember any talk about Pure Black Crystals around the games launch. Haven't even seen any screenshots, posts or links of an existing All-Black Crystal, you could be right but I haven't seen any proof to make think otherwise. I do still have some of my Pre-Order, Black-Yellow ones though.
It was a long time ago. All I remember is people got upset that a pure color crystal got retired after three months in game. Dunno if they were black, but I know it wasn't the ones we have now.