I don't keep black, gray or white on my palette. On the rare occasion that I need black, I enjoy mixing my own. Everyone has their favorite recipe for black. Mine is based on the Winsor Newton colors I always have on my palette. My black comes together with intense blue, purple lake, and burnt sienna. The intense blue is extremely rich and saturated and makes my black almost completely opaque. It's like painting with thick ink, and it's kind of odd for watercolor, which is the transparent paint medium.
So, about how I got to paint with black and orange on Halloween.... Completely unplanned.