If I'm reading this correctly, the nucleus of gold is so massive that it accelerates the orbiting electrons close enough to the speed of light that they gain su

If I'm reading this correctly, the nucleus of gold is so massive that it accelerates the orbiting electrons close enough to the speed of light that they gain substantial mass. The increased mass in the outer shell electrons allows it to have stronger, and therefore shorter bonds. This in turn, creates a yellow colour as opposed to the colourless silver (I assume because the shorter bonds change the way photons interact with it). I didn't understand why gold was similar to copper, while silver (between the two on the periodic table) is not. Does it have to do with how electron shells are filled? Definitely beyond my level of chemistry :-)