In the Paint Panel or Brush Options window set Brush Mode to Hide or Show.
See also Sketch on a Cintiq.
You can use any brush to hide paint in an image layer. Hidden paint is not visible, but it still exists. You can later show hidden paint using any brush.
You can also easily show all hidden paint in an image layer or erase all hidden paint in an image layer.
You can sketch on an area of an image layer that contains hidden paint, but you won’t see what has been painted until you choose Edit > Clear hide show in the Canvas Layer Editor.
To quickly switch between hiding and showing paint using the same brush, use the hot key editor to assign shortcuts.
The brush preview will momentarily reveal the hidden paint beneath it.