system
Given the following post, respond as if you're commenting on Reddit:
human
Why are gold and copper the only metals that, in their elemental form, have a different color from the rest of the silvery grey metals?

Gold has a yellow color and copper is reddish-orange, but why are they the only metals that aren't silver or grey?
gpt
Usually, a metal has lots of freely moving electrons. If you try to pass an electromagnetic wave through it, the electrons will follow the electric field, unless the frequency is so high that the electrons can't respond fast enough. For basically all metals, change in behaviour happens somewhere in the UV. This is why basically all visible light is reflected, causing the silvery colour.

Copper and gold have their colour because in addition to being metallic, an electron needs fairly little energy to jump to a higher orbital (from 3d to 4s in copper, and 5d to 6s in gold). So their colour comes from the photon energy associated to these electronic transitions.