Gold is the Sun. The symbol is a circle with a dot at its centre, which is also the astronomical sign for the Sun and one of the oldest ideograms still in daily use. In alchemical Latin the metal is routinely called Sol, and preparations of it are solar.
Unlike tin and Jupiter, this correspondence needs no reconstruction. Gold is yellow, it is bright, it does not tarnish, and it is the most valued of the metals; the Sun is yellow, bright, unchanging and the chief of the heavenly bodies. The reasoning sits on the surface of the thing, and the association appears in Egyptian, Mesopotamian, Greek, Indian and Chinese contexts independently of one another.
The physical basis of the colour is worth stating, because it is unusual. Almost all metals are silvery-white; they reflect visible light more or less evenly. Gold absorbs in the blue and reflects yellow and red. The reason is relativistic: gold's inner electrons move fast enough that relativistic effects contract the orbitals and reduce the energy gap between two particular electron levels, bringing the absorption down out of the ultraviolet, where it sits in silver, and into the visible blue. Gold is yellow because of special relativity, which is a fact worth having, and cesium and copper acquire their colour by related routes.
Gold does not corrode. It does not react with oxygen at any temperature, it is unaffected by water, and it resists every single acid. It dissolves only in aqua regia, royal water, one part nitric acid to three of hydrochloric, a preparation described in Arabic alchemical texts by the thirteenth century and known throughout the Latin tradition afterwards. The name says exactly what it means: the water that dissolves the king of metals. Gold's permanence is why grave goods come out of the ground still bright, and it is the physical fact standing behind every association of gold with incorruptibility and with eternity.