Nutty hair colors

Ancient Romans had as many as 100 different formulas of hair dye. Some of these formulas used charred eggs, leeches and walnut shells. Walnut shells are still used to this day in modern formulas. This brings me to the question: Who decided it was a good idea to dye pistachio shells red? And how do they make that dye?
I’m always wondering how to make this dye, and how to make that dye ;)