Yes, the melanin level and change over time. Different follicles on your head can even be different colors.
Yes.  The levels of pigment can change over time which is one reason young children often have their hair color change
I like brown hair Oh, it's second only to black hair in how common it is. Oh, I didn't know that. Is it different than other hair besides color? Yes, brown hair has thicker strands than blond hair but thinner than red hair. What about blonde? Blond refers to the color on males, while blonde is for females. At any rate, it has little of the pigment called eumelanin. Oh, really? Can a person's hair color change, besides going gray, of course?
Levels of melanin can vary over time causing a person's hair color to change, and it is possible to have hair follicles of more than one color on the same person.