Why is Gold Yellow And Copper Reddish?

Have you ever wondered why gold is yellow and copper is red? We see colour when light bounces of a surface. When light made of photons hits a metals' surface all wavelengths are absorbed. metals are not black because all wavelengths are immediately re emitted. If we look deeper. Metals are made of conduction band and valence band which overlap. Therefore, when electrons in the valance band gain enough energy from the photon they can jump to the conduction band, leaving the atom in an excited state. Then the electron falls to a lower state, releasing a photon with the same energy difference. why do we see gold yellow and copper reddish but not grey as other metals? This is because gold has a strong absorption of the violet wavelength. Thus the re-emitted photon lacks this wavelength. The result is that gold appears yellow. For copper the green wavelength is strongly absorbed. So copper appears red since it is the complementary colour of this wavelength. But why do these metals have a strong absorption of these wavelengths? The reason is due to relativistic effects where the energy levels experience a shift from the high frequencies to the lower frequencies. the transition responsible for this strong absorption in gold it is the transition from a 5d to 6s shell while for copper it is the transition from 3d to 4s. And that's how copper is red and gold is yellow.