I have no idea, but I can tell you that brown hair has more eumelanin and less pheomelanin.
Brown hair is this shade due to having high levels of the dark pigment eumelanin, and lower levels of the light pigment pheomelanin.
I have brown hair unlike my sister who is blonde Oh, interesting. Were you aware that brown hair is second only to black in commonality? yes.  it is strange - I wonder where red hair comes from
It is characterized by higher levels of the dark pigment eumelanin and lower levels of the pale pigment pheomelanin.