What is the Chinese herb that keeps hair black?

In the realm of traditional Chinese medicine and herbal remedies, there exists a deep-rooted belief in the power of natural ingredients to promote health and well-being. Among these, a particular herb stands out for its purported ability to maintain the natural blackness of hair. Could you elaborate on what this mysterious Chinese herb is? Is it a common household ingredient, or a rare and precious botanical? Does it require specific preparation methods to unleash its hair-preserving properties? Moreover, what are the scientific explanations, if any, that back up these traditional claims? And how effective is this herb compared to modern hair care solutions?