Allow me to fill in the gap with answering to why I paint on black. I can remember, as a young girl just starting to draw, I preferred using chalk or white pencil on dark paper. In my early 20's, I always used pastels or colored pencils on dark paper. Years later, when I started to paint again, I used acrylic on black. Oddly enough, I guess I've always preferred to do it that way in whatever I used. I guess early on I realized even a dull still-life or human skin 'emerged' out of the dark and made for a more interesting piece. I thought so anyway.
Another crucial point, for me, is I can see the colors more accurately when I paint on black - what goes down stays down. The result is that I rarely go back and rework any of it, which makes for a quicker process, which is a good thing.