Pigment molecules, just like any other molecule, have electrons that can "occupy" different energy levels. It turns out that in pigment molecules, the differences between certain energy levels correspond to the energies associated with specific wavelengths of visible light. Pigment molecules are often organic molecules (they have carbon) with what are called "highly conjugated rings" that allow electrons to "bounce" around when they get "excited." Many other pigments contain transition metals, and actually transfer electrons between multiple molecules.

But what does it mean for a molecule to "get excited?" Broadly speaking, what this means is that electromagnetic radiation (different kinds of light such as UV, XRay, and visible light) can hit a pigment molecule and confer energy to the electrons in the molecule. If there is enough energy transferred, the electrons are "excited," or "go" to higher energy levels. When the molecule's electrons "relax" back down to its original or "ground state" energy, energy is released in the form of visible light. I hope this helps!

There are many, *many* different kinds of pigments in existence, and they are made of different things. However, as for how they work:

Chemical bonds have energy levels, and these energy levels correspond to different frequencies of light. When a photon of the right frequency comes along to move a chemical bond from one energy level to another, the photon has a good chance of being absorbed. If the photon is of the wrong energy to move a bond between two energy levels, either not enough to reach the next level or too much so that it would overshoot the next level, the photon will likely not get absorbed.

I don't know how reflectivity works as well as I do absorption (reflectivity is more complicated), but I can tell you that the process is similar in that electrons in molecules are somewhat free to move and will absorb, then re-emit, the photon of the same energy. Metals are reflective because the electrons in metals are almost free, and have an infinitely large number of possible energy levels, and thus can reflect any photon.

Most pigments work by absorbing certain wavelengths of light. Other wavelengths are reflected or scattered, which cause you to see those colours. At the atomic level, certain wavelengths of light are of the correct energy to excite specific transitions of electrons in the molecules or the solid. The energy of the light is absorbed to excite the electrons, so it is no longer able to be seen by your eye.