Hello
How to proceed if I don’t want a metallic orange like the miror base but a color with roughness, any idea… 
You have to control the roughness of the shader by filtering your orange color to get a mask and/or use RGBcurve to adjust and put it into the roughness input of the principled shader (for example).
OK but is-there a way to make it “live”, without mask? Maybe your second option could work?
Question color.blend (946.6 KB)
I haven’t looked into the file but anyway if you want to have different materials you may have to assign them to different areas or mix them by any kind of mix control: vertex colors, vector computation, mask map…
You may have to look about the basics of materials??