Meta gems won't give you the stat boost unless you have enough of the right color of other gems equipped. Secondary colors count as both their primaries. For instance, if a meta gem needs two reds and a blue, it will be active if you have a red and a purple somewhere in all your equipped gear.

The raw, uncut meta gems are made by alchemists. Here is just a quick table of what goes into them.

Name	Materials
Earthstorm Diamond	3 Deep Peridot, 3 Shadow Draenite, 3 Golden Draenite, 2 Primal Earth, 2 Primal Water
Skyfire Diamond	3 Blood Garnet, 3 Flame Spessarite, 3 Azure Moonstone, 2 Primal Fire, 2 Primal Air