In the mid 19th century, we began to learn how to create molecular orbital colors ourselves, though we learned how to make the colors before we really understood the mechanism. It suddenly became a colorful world. In metals, all free electrons are alike, a condition called degeneracy . The Pauli Exclusion Principle causes these electrons to assume all energy levels up to some maximum value. Above that maximum energy, called the Fermi Surface, are unfilled energy levels.
Any visible photon can find an electron to excite.
Thus metals are opaque. The excited electron falls quickly back to its ground state, emitting the same wavelength it absorbed. Thus metals are highly reflective. Most metals, like this silver, have energy levels uniformly-enough distributed that all wavelengths are equally affected, so the metals are neutral in color. Some metals, like copper or the gold shown here, have unevenly distributed available energy levels.