I saw that once at the local shop where plastic and wood parts are restored. The guy covered the entire top of the ball with some sort of wax, then, with a sharp needle that was warmed up, he removed the parts that were to receive the white paint and he sprayed the white paint and waited till it was dry. Good point of that is that he didn't put the white paint till he was satisfied with the looks of the shapes, as that part of the process is reversible.
After repeating that a few times, the white numbers looked like embossed and then he just removed finally the wax.