The Fresnel effect is wavelength dependent. It behavior is determined by the
index-of-refraction of the material (taken as a complex value to allow for attenuation).
This effect explains the variation in colors seen in specular regions particular
on metals (conductors).
It also explains why most surfaces approximate mirror reflectors when the
light strikes them at a grazing angle. This version of the equation ignores
the polarization of the incoming and reflected rays.