This is a beautiful technique, but also the most time-consuming one. That is because it requires to spray-paint or to put tape on every single domino. FlippyCat thought of a simple, but effective solution: You put a long duct tape on a bunch of dominoes and all you need to do afterwards is divide the dominoes.
IIIIIDominoIIIII, on the other hand, simply sprayed black varnish on their dominoes. The big disadvantage of that method is that you cannot change it back.
And the video by FlippyCat: