Meta GemsFollow

First off I apologize if this topic has already been covered and I just couldn't find it. I just recently started to get my pre-kara gear together<thank you for guide Aeth>and saw that some of my gear has meta-gem slots. My question is how this work. I see that it say requires x amount of red, blue etc. but not sure exactly what that means. I'm sure once you answer I'll sound a loud "DUH" but I appreciate the help. Thanks!

There is only one slot where a meta-gem slot can be (at least until now) and that is the head slot.

You put a metagem into the slot as you put a gem in a normal socket. However the metagem will only work once you have met the metagem requirements (e.g. at least 2 blue and at least 2 yellow gems).
Those requirements are met if you have so many gems equiped in the gear you currently have equipped.

For hunters use this if you can afford it and the item is of good quality.
If you want to be cheap, use this one.

On a sidenote. Mixed-Color gems count as both colors. That is to meet the requirement of at least 2 blue and 2 yellow gems you can put in two of these and the metagem requirement is already met and you can socket the rest of your gear with red gems.