They said there was 3 palets but can we forge on any map still?
Yes, you’ll be able to use the forge mode in every map but there are three unique pallets for three maps built specifically for forge. It’s the same as Halo 3 - Sandbox, Foundry, ect. 
I’m so happy to hear we have three pallets! I wasn’t even expecting two! 
I don’t think what he’s saying is that you can only forge and set maps, I think it’s more of he’s saying there are 3 forge world like maps. But don’t quote me on that, I’m just going by the seat of my pants on this one.
Unknown, but I love how they specifically said that the Forge maps wouldn’t all look the same.
To my understanding, we will be able to forge on any maps, EXCEPT there will be three forge exclusive maps. Its just to give us some variety while forging. For example, In halo reach while we had a lot of options at our disposal, things got bland after a while whether it be the grey pieces or the repetitiveness of forge world.
With three different maps, we have options on where we can forge and what we can forge.
And I mud say, the pieces and environments look stunning…