Great thanks for recommendation

To add to Tobias' explanation, the term "localized" is of crucial importance here.

In small nanoparticles, the plasmon is localized because it cannot propagate. In that case, the resonance is at a different energy than the surface plasmon resonance in the bulk. So, even if surface plasmon resonance can be as high as 10-15 eV, the localized surface plasmon resonance in NPs can be at much lower energies depending on the material, shape and size of the NP.

For small (20 nm) spherical gold nanoparticles, the resonance is around 2.4 eV (520 nm). Unlike Tobias' response however, it is not the scattering that give their color to small gold colloids (< 40-50 nm), it is mostly the absorption of the particles (they absorb green light and some of the blue light, so most of the light that is trasmitted is red). The scattering for such small NPs is too weak to have a notable effect on the color of the solution.

For larger particles (>50 nm), the scattering is stronger and contributes to the color of the solution.

The best read to understand more about that is Mie Theory. You can also have a look at those books which have good discussions about optical properties of noble metal NPs:

Kreibig & Vollmer, Optical Properties of Metal Clusters (1995)

Le Ru & Etchegoin, Principles of Surface-Enhanced Raman Spectroscopy and related plasmonic effects, (2009)

As for the relation of the color of the colloids and the color of the bulk, there is indeed a relationship; it can be seen mostly by looking at the dielectric function of the metal. In the case of gold, the interband transitions happening at 2.5 eV and higher energies affect the reflectivity of the bulk (reflectivity is low at wavelengths below about 500 nm and almost 100% at longer wavelengths, resulting in the yellow color).

For the NPs, the same interband transitions have a strong effect on the position of the localized plasmon resonance. If you compare silver and gold, they both have similar dielectric function apart from these interband transition that happen at higher energy (4 eV) for silver. In the case of silver the localized plasmon resonance is at 3 eV and for gold because of the interband transition, the resonance is "pushed" to 2.4 eV.

In both the color of the bulk and the color of the solution, the interband transitions have a strong effect.

I hope these explanations will help you.