Radish drawn with Brushes on my iPhone. I heard about this app from designer Tim Copsey of Empty. I checked to see what Hockney uses and it was the same one.

White paint

I went to two exhibtions at the Tate Modern, Arshile Gorky and Theo Van Doesburg and noticed one thing in common with their paintings. Rather than leaving the neutral colour of the paper or canvas visible, they painted it in. If they wanted white they painted white, in oil or gouache.