Slate blue

Can you please explain what he reffer when saying "this one" and also what is "slate" in this context?

And see the cabinetry is nice solid, newer sink, new faucet. We painted this one a dark slate blue. Reason for that is because as you see we have the side door right here

I add an image from the video and video with exact time thanks

https://lh3.googleusercontent.com/7FkvL2QttQcVQ_NcF5eCHocCOqfwzZshclD_VXrfocuqXlClxw_cR_h8N4_usXOySAYh=s142

(From video 1:34)