Re: What determines the colour of copper

The color that any material presents to us is based on the manner in which 
light photons interact with the electrons in the outer orbits of the atoms 
that conpose the material.  In the 3rd edition of the college textbook 
Advanced Inorganic Chemistry written by Cotton and Wilkinson, on page 65 
it is stated that "the properties of metal such as high reflectivity, 
eletrical conductance, thermal conductance, and mechanical properties are 
derived from the structural and electronic nature of the metal".  The 
atomic weight of the metal would not be a factor in the color of the 
metal.  The color will depend on the energy level of the electron orbits 
that interact with the photon of light.  If the electron density of the 
material is high enough the light could be considered to "bounce" off of 
the atom and the color of the light not changed.  If the energy of the 
light is high enough to interact with the electron shell then depending on 
the energy of the electron shell a certain color of light will be absorbed 
and the other colors reflected.  When the copper reacts with other 
elements the electronic structure of the copper is changed and the color
(energy) of light that the new compound reflects changes.  Oh, remember 
that the color of a light photon corresponds to it energy. For example, 
red light is less energetic than blue light.  Green light light lies in 
between. Thats why UV light (ultra-violet, or very very blue light) which 
is very energetic can cause damage like sunburns to our skin.