If you use a black and transparent brush texture, on the object on which you paint you’ll get black from the black areas, and you’ll get no color from the transparent areas, whatever color you pick on the palette.
If you use a black and white brush texture, on your object you’ll get black from the black areas, and from the white areas you’ll get the exact same color you picked on the palette.
So in both cases you can’t get any color from the black areas. Actually in the video he doesn’t get any color from the black areas, he picks red in the palette and gets red from the brush texture white areas.