It's actually the bottom of the wall planters themselves. I used to run a similar set up with my tank and that's what they looked like. The tricky part is making sure when you free float them they're well away from any walls because otherwise they'll snap right too them no matter how they look before you exit the housing interface.
As for the brown part, would you believe me if I told you that was the back of the eorzean map because I'm fairly certain that's what they're using. I could totally be wrong and it could be something else but I've seen them used as false partitions before for just that reason.
