This is a very neat idea from the folks at Dead Design. They call these optical illusion control surface masks. The idea is to apply the masks and then spray a light or darker variation of the color of the control surface. It is suggested that the color used be a highly diluted shade of about 5% color. It is also recommended that any raised detail be sanded smooth prior to application.

As you can see, the set provides both sides of the ailerons, elevators, and rudder. These are designed for the Fine Molds 1/48 Ki-43, but you could probably use them on the Hasegawa or Otaki kits if you are sanding smooth any extant detail. A more complete set if directions is available on their web site if you want to see how this is done.