I tend to think the wings *do* have a fade in the 3D model. But it is not all the way from black to white, more like black to grey.
One additional possibility to consider is that the fade can be done with decals if you have solid black on one side, and when not dealing with compound curves.
One additional possibility to consider is that the fade can be done with decals if you have solid black on one side, and when not dealing with compound curves.