Short answers, pulled from the story.
The word comes from the Old French alborne, meaning blond, which in turn derives from the Latin alburnus, meaning off-white or whitish. Despite these pale origins, by 1430 it was being used in English to describe reddish-brown hair.
Titian hair is most commonly described as brownish-orange, whereas auburn is specifically defined as including the actual color red. The two are often confused in everyday use, but auburn sits closer to red on the spectrum.
Auburn hair results from a combination of pheomelanin, which contributes red and yellow tones, and high levels of eumelanin, which contributes brown and black tones.
Auburn hair occurs most frequently in Scandinavia, Britain, Ireland, continental Germanic Europe, northern France, Poland, Russia, and Egypt. It is less common further south and southeast but can appear regularly across Southern Europe.
Early scribes and typesetters found the word unstable. Pre-1685 folios of Coriolanus, Thomas Kyd's Soliman and Perseda from 1588, and Thomas Middleton's Blurt, Master Constable from 1601 all use the corrupted form abram instead of auburn.