Black "Gems" tiles
 

There are several different "blank" gems in the /gems game.

I think I remember there being one blank gem, but when I play gems ingame the blank ones don't always remove each other, making me think that there's just a graphic missing for some of them.

yeah, that is because the game uses the luclin spell gems, and we use the classic spell gems ... if you use the luclin spell gems you can play gems, even thou your spell gems are ugly as hell then :p