Based on the provided reference, hair oils enriched with Bhringraj, Triphala, and Vibhitaka are known for preventing premature hair greying. This suggests they help maintain melanin in the hair, rather than directly increasing it. The reference focuses on preservation and control rather than direct melanin enhancement.
While the reference doesn't directly state which oil increases melanin, we can infer that oils preventing melanin loss could indirectly help maintain natural hair color.
