Very black eyebrows give the face an intense and searching expression; when natural they accompany a passionate temperament. Very light eyebrows rarely are seen on strongly intellectual faces, although the color of the eyebrow is not accepted singly as denoting lack of intelligence; the form gives the key to the faculties and their direction.
Red eyebrows denote great fervor and ambition; brown a medium between the black and the red.
Harriet Hubbard Ayer’s Book, 1899
Physiognomy, or the judgement of a person’s inward characteristics by their outward ones, was popular in the 1800s, though forms of it had been around for much longer. What do your eyebrows indicate about your temper or character?
Don’t worry… the same source goes on to give instructions on how to change the color of your eyebrows, so apparently nature does not have the last word!