graying

This term describes a gradual transition rather than a sudden change. When used as an adjective, it emphasizes the ongoing process of losing pigment, often carrying a connotation of aging, maturity, or the passage of time. It is most frequently paired with specific areas of the head, such as temples or sideburns.

As a noun, it refers to the biological phenomenon itself. Because it describes a continuous process of change, it is treated as an uncountable mass noun. You would not refer to "three grayings" of hair, but rather "the graying" of hair.