If you’ve ever seen a mummy in a museum, you might have thought the ancients went a little overboard with henna and other red dyes. While people have colored their hair practically forever, it’s more likely what you’re seeing is the change in hair color that occurs after a person dies.
The color of hair comes from the mixture of two melanin pigments: eumelanin (yellow-brown-black) and pheomelanin (red). Pheomelanin is more stable, so over time the eumelanin oxidizes while most of the pheomelanin remains. This is reason most Egyptian mummies appear to have reddish hair. The change occurs more slowly under dry oxidizing conditions, such as burials in ice or sand, than under wet reducing conditions, such as burials in wooden coffins or damp caves. Therefore, you would expect to see a more faster or more dramatic hair color change in a body from the jungle, for example, than a corpse from the desert.