Do people who have red hair eyebrows?
Red hair is caused by a mutation in the melanocortin-1 receptor (MC1R), which reduces the amount of eumelanin (dark brown/black pigment) produced and increases the amount of pheomelanin (yellow/red pigment), resulting in red hair. Often, when a person has the genetic mutation that results in red hair, they also have variations in the genes controlling eyebrow colour, resulting in red eyebrows.
However, genetics can be unpredictable, so some redheads may have different eyebrow colours due to other genetic factors.