optics - Light-matter interaction and an object's appearance

I am taking a course in Computer Graphics, and the teacher said we could put materials in there main categories:

• mirror like


• glossy or specular



• diffuse

He suggested that the law of reflection is immutable and applies to all types of surfaces but that glossy and diffuse surfaces appeared the way they do because of their microstructure. The roughness of these surfaces causes light rays to be reflected in random directions, thus blurring incoming light. So far, so good.

He also insisted on the idea that surfaces (expected in the case of metals) reflects the incident light color. In other words, if the incident light striking a mirror is white, reflected light is white (and not yellow as it is with gold, but again metal is a different case).

What I don't understand is that: if you use "roughness" to explain why some materials are shiny and others diffuse, diffuse surfaces too reflect incoming light color as mirror surfaces do. Therefore if mirror like surface do not have a color of their own (since they only reflect the incoming light color) so should diffuse surfaces. But diffuse objects have a color of their own (which mirror surfaces don not have). Thus, there's a flaw in the reasoning which I can't resolve.

I understand the object's color comes from the fact that electrons making up the atoms the material is made of, selectively absorb photons of some specific wavelength, and reflect the others. However does it mean it reflects these photon always in the mirror like direction? How and why does that happen that way if this is the case?

I am trying to put in one single pictures all the pieces of the puzzle together. Light can only be either reflected or refracted, however objects are coloured because they absorb some light frequencies, but I am told that "mirror reflection" does not affect the incident light color (in other words, that the reflected light color and the incident light color are the same in the case of mirror like reflections).

I am totally lost and would really appreciate if someone could shed light on this mystery.