Painting technique I read about

The black undercoat with white over the high areas is a way to bypass washing to get a lot of depth. Main color over white brings it up strongly leaving deep shadows. Inks over the main colors give them variation.  It makes the deep areas starker in contrast than you get washing after colors.

Is a good way to work.  I don't know if it saves much time, because you still have several steps that need to dry in between.  I does do away with blacklining to define panels and features.