18k yellow gold is generally very stable and resistant to color changes. However, there are a few situations where you might notice slight changes: Tarnishing: While 18k gold is highly resistant to tarnishing, it can happen over time, especially in humid or polluted environments. This can make the gold appear slightly duller. Patina: Over many years, 18k gold can develop a slight patina, which some people actually prefer as it gives the jewelry a vintage look. Surface Dirt: Accumulation of dirt, oils, or cosmetics can make the gold appear darker or duller, but this isn't a true color change and can be cleaned off. Rhodium Plating Wear: If the 18k gold has been rhodium plated (uncommon but possible), the plating can wear off over time, revealing the yellow gold underneath. Skin Chemistry: Some people's skin chemistry can cause a slight darkening where the gold is in contact with the skin, but this is usually temporary. In general, any noticeable color change in 18k gold is likely due to external factors rather than a change in the gold itself. Regular cleaning and proper care can help maintain its original color.