No, it is not true that liquid gold and copper are the only liquid metals that are not silver in color. While it is correct that liquid gold and copper have distinctive colors, there are other liquid metals that also exhibit different colors.
Liquid mercury, for example, is silver in color, similar to many other liquid metals. However, liquid gallium is known to have a silvery appearance when it is held in a container but can appear to be somewhat golden when in larger quantities due to the thin oxide layer that forms on its surface. Other liquid metals such as liquid lead, tin, and bismuth also have varying colors.
The color of a liquid metal is primarily determined by its electronic structure and the way light interacts with it. Factors such as the arrangement of electrons in the metal's atoms, the energy levels of the electrons, and the presence of any oxide layers or impurities can influence the observed color.
Gold and copper, specifically, have unique electronic structures that give rise to their characteristic colors. The color of gold is due to its unique electronic transitions, which result in its distinct yellow color. Copper, on the other hand, appears reddish-brown due to its electronic properties.
In summary, while gold and copper are well-known for their distinct colors when in liquid form, there are other liquid metals that also exhibit different colors, and the color of a liquid metal is influenced by various factors including its electronic structure and the presence of any surface layers or impurities.