Short answers, pulled from the story.
Brown hair is the second most common human hair color, ranking behind only black hair. It ranges from light to dark brown and comes from moderate levels of eumelanin with no pheomelanin present.
Eumelanin gives brown hair its color, present in moderate amounts. Two forms of eumelanin exist, black eumelanin and brown eumelanin, and the balance between them along with pheomelanin determines whether hair reads as brown, black, grey or blond.
Brown hair predominates across most of Europe and is also common in North Africa, the Middle East, Central Asia and South Asia. It appears widely among East Asians, Australian Aboriginal peoples, Melanesians, and populations across the Americas, including the Southern Cone, Colombia, Costa Rica and Puerto Rico.
Brunette comes from the French brunet, a diminutive of brun meaning brown or brown-haired, whose feminine form is brune. In modern English, brunette lost its original diminutive sense and now typically describes a brown-haired woman, while men are usually called brown-haired instead of brunet.
In Spain, 57 percent of people have brown hair. Among the remainder, 7 percent are naturally blonde, 26 percent are brunette, 3 percent are redheads, and 10 percent fall into darker or lighter brown categories.
In Western popular culture, brunettes are commonly stereotyped as stable, serious, smart and sophisticated, sometimes framed in rivalry with blonde women. Well-known brunette figures include the Lady of Shalott in paintings and the woman in Leonardo da Vinci's Mona Lisa, while Anita Loos wrote But Gentlemen Marry Brunettes as a sequel to Gentlemen Prefer Blondes.