Real gold should not tarnish or become discolored in any way. The jewelry, however, may cause black smudging on the skin.
Gold jewelry can last for many years if it is properly cared for. It should not tarnish or rust. The gold can cause smudge marks to appear on the skin of some wearers. This does not mean it is not real gold and is more likely to happen with 10 karat gold compared to a higher karat. This is because of the additional alloys in the jewelry. It is a reaction between the metal and the skin of certain people. Some chemical products can also cause the marks to appear.