Hey,
I heavily use (like many others here) Siger's Complex Fresnel for realistic Metals.
Metals are ment to have 0 RGB Diffuse, unless you want rust and grime mapped over it.
However, due to how Complex Fresnel works, it reveals the diffuse influence at certain angles, meaning now Diffuse Color actually does influence how the metal looks. Make it white, its brighter, 0 RGB and its darker.
How is it meant to be properly used?
0 RGB like always?
1 RGB to prevent energy being swollen artifacts?
Default Grey?