What colour hair you have is determined by the type of melanin you have, there are two types: eumelanin, which is dark brown or black, and pheomelanin, which is reddish yellow.
Red hair ranges from light strawberry blond shades to titian, Copper, and less commonly "true" red.
Red hair has the highest amounts of pheomelanin, around 67%, and usually low levels of eumelanin. At 1-2% of the population, it is the least common hair colour in the world. It is most prominently found in Scotland and Ireland. Scotland has the highest proportion of redheads; 13 percent of the population has red hair and approximately 40 percent carries the recessive redhead gene.