How to add layer in board geometry？

How to add a new layer in board geometry?
You can find board geometry : display--->color\visibility---->board geometry
Thanks

I just find how to add new layer in board geometry:setup--->subclasses, then ok

that's too easy, so, nobody want to give the description. mabye,sorry

Why do u always speak sth in English?
Maybe if u descripe it in Chinese,someone can answer it easily.