Over time, it’s normal for e-liquids to undergo oxidation, causing the nicotine to interact with the flavourings, resulting in a deeper yellow or brown colour. This process, known as steeping, is common and indicates the e-liquid’s age. A colour change, particularly if the e-liquid is within its expiration date, is not a safety concern. In fact, many vapers find that the flavour improves after this colour shift, as the steeping process enhances the depth and richness of the taste.