[grey_whiskers]

Thanks for the courteous reply.

I too went into software development after cutting my teeth on the Crays at U. of Minnesota. Gas-phase molecular scattering theory.

I seem to recall a symposium at a theoretical chemistry conference that the color of gold is due to relativistic effects on the inner electrons. Too bad I wasn't taking notes :-)

PS Love your line about a libertarian estimate.

Cheers!

[BMCDA]

I seem to recall a symposium at a theoretical chemistry conference that the color of gold is due to relativistic effects on the inner electrons.

Actually it's due to interband transitions. In copper for instance, electrons from the filled 3d bands can transition to unoccupied states in the 4s band above the Fermi level. Thus, above a threshold of ca. 2eV, the reflectivity decreases drastically.
Gold has a slightly higher interband absorption edge which is the reason why it has a yellowish color as opposed to copper with its reddish tinge.
Silver on the other hand has no color (i.e. reflectivity is pretty high and constant over the whole visible spectrum) because it's threshold is at about 4eV which is in the ultraviolet region of the spectrum.