Knowledge: The level of wrinkles will change as you get older due to sun damage. However, the percentage of pheomelanin of hair does not alter as a human ages.

Conversation:
I have brown hair, quite common I guess.
Yes, it is below black hair for most common hair color.
And what is the least common hair color?
Red hair naturally happens in 1 to 2% of the human population although I'm not sure if it is the least common hair color.
I say 1 or 2% probably makes it the least likely. Do you know what makes hair dark like my brown?
It has to do with pigment. So high levels of eumelanin makes the hair dark while lower levels of pheomelanin make the hair lighter.
Interesting.  Can the level change as you get older?

Response: Ah. No, the percentage of pheomelanin of hair does not alter as a human ages.