The other day I heard a peculiar bit of information about red hair on a BBC 4 programme titled Castles: Britain's Fortified History. It came in a section about making swords. The interviewed blacksmith stated that it was written that "the urine of a ginger virgin boy" was used in the tempering process.
I've previously noted another variation on this story about the urine of red-haired boys being used in the making of stained glass windows. I think it maybe intertwines with the alchemical process of turning one metal to another - hair colour, blondes and reds, symbolising various metals, most notably gold.