Colorpict and values for reflectance, specularity and roughness

I know that for generic plastic material, the third raw contains values for reflectance, specularity and roughness.
As I will use colorpict to render a textured object imported from an obj model I wonder what happens with those values when a picture is applied. Is it just reflectance affected and in which way?

Thank you for your kind help!

The Radiance reference manual is the place to look for this kind of information:
Under the entry for “plastic,” it says “A pattern modifying plastic will affect the material color.”
There are other important documents linked to the parent page at: