So, I've been messing around with skin subsurface scattering shaders for about a day now. I'm roughly following this tutorial, by CGBlender, (links to both .blend files at the bottom) with elements from Andrew's PBR Dielectric Tutorial.
I've almost entirely gone my own way with the material, the main difference being that instead of giving the subsurface scattering nodes different colors, I gave them all the same color, but each has a radius that only scattering certain colors.
Now, for my question: what is the most physically accurate way to mix "layers" of SSS. In other words: I want to know how to mix the different layers in order to create the appearance of layers of skin, fat, and blood. Sidenote: I haven't yet added a third SSS node, so I only have representations for blood and fat, with diffuse acting as the skin. The fat and blood layers are being controlled by a simple factor slider.
P.S. don't hesitate to tell me if I'm doing all of this entirely wrong, and please lead me in the right direction; I'm pretty much winging this.
Any help is appreciated :)