we present a small advance in Thea material system, useful for those that aim for extra fine details when rendering.
This advance is about the coating absorption that can be wavelength dependent. The central idea is that the user defines now the absorption color at certain depth inside the coating (typically, 100 micro meters) using a standard color/texture control. This color becomes then the dominant one for any reflections coming from layers underneath.
Since the actual distance traveled by the reflected rays varies with the angle, the colored absorption creates a subtle but still observable effect where there is a simultaneous hue and saturation shift. The effect is "indeed there in real life" and can be seen in cases like metallic car paints and tinted wood varnish.
I attach two renders of a model, where you can see the transition and hue shift with viewing angle. This is more evident as you see nearer the edges of the car.
