Whenever a scalar value is hooked up to a material property it is handled as a gray scale value. However in 4.5 a scalar value in the subsurface input is now handled as a color value with the scalar as the R intensity and zero for the G and B components.
As a result older materials are now rendered more red then they should be:
https://dl.dropboxusercontent.com/u/3284052/SSS4.5Bug.png
This applies to the Subsurface and Preintegrated skin shading models. The new Subsurface Profile works as expected.