Should ideal specular multiply light colour with material colour?
What "ideal" means in this context is that there is no divergence in the direction of light reflection vectors (i.e. no roughness) but that they are all considered to be perfect reflections from an optical flat surface. However, even for optical flat surfaces Fresnel equation is still applied in BRDF evaluation that changes specular reflection and is potentially wavelength dependent, which is a common characteristic with metals.



However, in smallPt there's no Fresnel approximation (e.g. Schlick's approximation) but the surface reflectance is simply multiplied with constant term which is wrong. Also 0.999 specular albedo is very high for any real material. Below is a table of specular reflectange of various metals &amp; dielectrics at normal incidence for reference: