There are several ways to make a material have color.
Local origins of color
The electons in molecules are layered over one another since they are fermions and thus obey paulis exclusion principle. Light can only be absorbed when at least the energy to the next higher allowed energy level is reached (and some further restrictions are obeyed). In simple molecules like dinitrogen (air) very high photo energies are needed to excite an electron (hard UV?). The problem is that the excited electron was responsible for the bond between the two atoms so the molecule falls apart. [Todo: check out dinitrogen LUMO  there seems to be "stable" N2*]
Creating chains of double-bonded carbon atoms creates a big shared space for the participating electrons. Since they now have more spacial freedom according to heisenbergs uncertainty principle their impulse can be smaller. This has the nice effect that you gain some energy levels that are higher than the unexcited "sea level" of molecule orbital electrons but are still low enough such that the electrons still fulfill their responsibility of holding the molecule together. The shape of the molecules may change though sometimes. Linear chain like molecules may be hard to mechanosythesize due to their lack of stiffness (or not).
Visible light with its low energy can be absorbed by lifting electrons into these intermediate energy levels. The remaining light appears in a certain color.
At the short blue wavelengths such chains become so short that the discreteness of the number of bond becomes problematic. Metal complexes where the photons either lift an electron to the from the complexed metal atom to the chaltrate ring or vice versa can do that. They may contain somewhat scarce elements like copper though. If it turns out it's impossible to arrange abundant atoms (possible unnaturally highly strained) such that they absorb short wavelength there are still other methods to make something look blue.
[note 1] also known as HOMO - for highest occupied molecular orbital) meaning that
Bigger scale origins of color
Color form wave interference
- like the ones butterflies use or simpler ones like ...
- Wikipedia: Structural coloration & Iridescsnce & Diffraction gratings & Photonic crystals
- Wikipedia: Interferometric modulator display
Color from plasmonic surface effects
[Todo: check inhowfar quantum dots are related]
Metallic reflectiveness is not exactly a color but if certain wavelengths are absorbed the reflected light can take on some color like present with copper and gold. The used materials need to have metallic conductivity. See wikipedia: plasma frequency
- Diamond raman lasers.
- Transparency and translucency (also called pellucidity or diaphaneity)
- Tanabe Sugano Diagrams - diagrams to determine the color of crystals (leave to wikipedia)
- Luminescence => Photoluminescence => Fluorescence & Phosphorescence
- quantum dot display. Even at room temperature quantum effects of electrons often work on a scale significantly above the single atom level thus atomically precise manufacturing is not needed (but usable) to make light emitting quantum dots. These are already in displays today (state 2016-12). (TODO: check rare element usage avoidability)