Tubed White is not a color!!! Tubed Black is not a color!!!! Therefore, Tubed Black and Tubed White used together are NOT colors. Zero plus Zero does not equal One.
Now, before someone decides to get offended by this - the white and black that companies manufacture, across the board, are flat and dead unless color is added to them. Any of the darker colors added together make gorgeous, living blacks. And yes, black can be added then to darken if necessary. Likewise, just a tinge of color added to White makes a rainbow of lights and grays.
I can see this from across the room! The black and/or white stand out as flat, empty and dead! In nature, black is filled with color!!! White is filled with color.
Until I studied with Helen Van Wyk, I was taught never, ever use Tubed Black because the Black would overpower any color it was mixed with. This is true of Mars Black and Lamp Black - they are opaque and muffle any color mixed with them - hence they are not on my legal list of colors. Ivory Black, on the other hand, is transparent and makes a million galaxies of gray. Beautiful gray, another dimension to our palette of colors.
I use Zinc white - mostly because Helen Van Wyk used it but I find it warmer than Titanium White. And, because our whole earth is warmed by the sun, I go with the warmer white.