Role of hair in Tangled:
At the beginning of the film, it is stated that the hair gets its power from a magic golden flower. This magic golden flower was used to heal a sick pregnant queen, who gives birth to Rapunzel. Cells from the flower went into Rapunzel making her hair glow and heal the sick just like the flower did. Mother Gothel, a witch, who found the flower before the Queen did, used it to make herself young. It is said she's used it for hundreds of years. When the queen used it, Mother Gothel wanted to get it back, so she broke into the palace and cut off a lock of Rapunzel's hair to keep for herself. But the lock turned brown and lost its power. So she kidnapped baby Rapunzel to use it for herself. She raised Rapunzel as her own and would not let her go outside of the tower (where she was locked away in) so that no one could take her or damage the hair. At the end of the film, all her hair is cut off, leaving it in a brown pixie cut.
Rapunzels hair is gold, and about 70 feet long. When cut, it turns brown. In the middle of the movie, after Rapunzel escapes her tower, it gets braided with flowers.
On Rapunzel dolls, her hair is long and blonde again. Not like how it was at the end of the movie, short and brown. Some dolls have her hair braided with flowers, and other just long and blonde. There is only one doll that has been seen with short brown hair. In pictures, Rapunzel's hair is again, long and blonde.
At Disney parks
At Disney parks, Rapunzel has her hair long and blonder, braided with flowers. Many ask Rapunzel during meet and greets why her hair is long again. Rapunzel apparently says "I had enough magic in my tears to grow my hair nice and long again." She says this because at the end of the film, after her hair is cut, Rapunzel finds that she also has magic tears. This is an excuse to grow her hair back.