I'm currently learning in my E-M class about the phonomenon of absorption, and I'm trying to figure out why we see what we see, but there are gaps in my understanding. Regarding insulators: Depending on the composition of the material, there are various "absorption spikes" that will "kill" the waves of certain frequencies as they try to penetrate the material. But the material is pretty much transparent to to rest of the frequency spectrum. For exemple, since paper appears white, I conclude that there are no absorption spikes in the "visible range" of frequencies. And I can also speculate that the sky is blue because every visible frequency appart from blue is absorbed by the atmosphere. But absorption cannot be the whole story, because for a metal, as a wave tries to penetrate it, every visible frequency is attenuated approximately equally and for all practical purpose, dies completely imediately after penetration. So the caracteristic color of metals must come from a phenomenon happening as the wave reflects from the surface! I am aware that the index of refraction for a metal and a dielectric is frequency dependant, but I don't have time to see how it makes the reflection coefficient behave, so I thought it'd ask on PF for a qualitative description. Are there frequencies that are entirely transmited? If so, are they the same that are entirely absorbed (in the case of a dielectric), etc. Thanks for any insight!