Operating system: Window 10 64bit
Graphics card: Nvidia GT-740
Broken: Blender 2.80 Beta, 2019-01-11 23:51, Hash: ce3475f74794 || Eevee
Worked: Blender 2.80 Beta, 2019-01-11 23:51, Hash: ce3475f74794 || Cycles
Short description of error
Unable to use RGB values in any form as input to Subsurface Scattering Radius input socket in Eevee, can still multiply values to change size.
Cycles has no issues with this input, so I believe the method is valid.
Exact steps for others to reproduce the error
For quick view:
Open attached .blend file. Set to Rendered Preview, notice there is red SSS in preview despite the input color of "Scattering Color" being green. Switch to Cycles, notice that the green value is displayed properly. Switch back to Eevee, change the color input of "Scatter Color" to any color you like, notice that the only thing that may have changed is the size of the scatter, not the color.
For simple reproduction:
In a new Blend file, set Rendering Engine to Eevee, in the Scene Settings, check the box labeled Subsurface Scattering, create a UV Sphere, shade smooth, and create a Sun lamp, open a Shader Editor so that you can still see the 3D View, set preview to Rendered, create a material utilizing the Principled BSDF node, set the Subsurface value to 1, notice that SSS should be working now, attach an RGB node to the Subsurface Scattering Radius input, change the color of the RGB node to any color you like, notice the color does not change, switch Rendering Engine to Cycles, notice the color value you selected earlier now appears in the render.