Quote - "It changes in surprising ways as the viewing angle becomes more shallow."

Fresnel in action. In metals the amount of reflected light is a function of the incidence angle and the wavelength. To achieve this effect you need to have a Fresnel function for each RGB channel with different parameters.

Dielectric materials don't change the color of the reflected specular light, so a single Fresnel function for the three RGB channels is enough.

Stupidity also evolves!