This early 20th century depiction of Sif shows her with long blond hair.
Sif is a goddess in Norse mythology. She is the wife of Thor and mother of Thrud and Ull.
Sif has hair made of gold. It grows just like normal hair. Her original hair's color looked like wheat. Loki cut off Sif's hair as a prank. When Thor found out he made Loki have golden hair made for her by the Dwarves.