Defines how much you want your subsurface color to be visible. If you set this to 100 % it completely replaces the surface color.
Subsurface Color (Color)
The subsurface color you want under the surface of your material. The quantity of visible subsurface color is defined by the following two options:
How far "into" the surface before the subsurface color is seen. If you make this value larger than the object that uses this material then the subsurface scattering will not be visible.