What exactly does the radius vector value on a subsurface scattering (SSS) shader do? In his SSS tutorial (making realistic bread), Andrew Price says that the XYZ values translate to the RGB values of the scattered light. But a lot has changed with SSS since that tutorial was made and that doesn't seem to be true anymore.
It does seem to have something to do with the scattering color, but it is not a simple XYZ to RGB thing. Here are a couple renders I did:
(the sphere is 75% SSS and 25% white diffuse)
So [1 1 1] seems to be just white scattering, while a [0 1 1] vector gives a turquoiseish color. Setting it to [1 0 1] gives a pinkish color and [1 1 0] produces a yellow scattering.
Intuitively, I would think that radius would mean the distance that the rays are scattered from where they hit the surface. But that would not change the color of the scattered rays and could be accomplished easily enough with a scalar value as opposed to a vector.
I am looking for a technical, mathematical explanation of exactly what the radius value does. I think I have a pretty good grasp on how SSS works, but it wouldn't hurt to explain that as well.