I'm trying to build a reasonable skin material and most of the implementations online seem to use the mix material to blend in different scattering layers of the skin and build specular on top.
I find the blend of all diffuse/scatter properties with a specular layer on-top using a mix mode to be not only physically wrong but also challenging to even fake a good balance between the two.
By doing a straight up mix we're effectively reducing the diffuse contribution (making it seem darker) and blending in spec which is also not at the energy level it needs to be. So overall, energy conservation is out the window.
The correct way would be to blend considering the spec albedo such that light that didn't reflect scatters into the skin. Even an "add" mode in the mix material would be better then just doing a mix.
Any future plans to make changes to how you blend materials or alternatively support a more rebuts way of rendering more complex organic materials such as skin?