Why does red hair dye fade in a few weeks, brown come out over time, and black dye not fade at all?

Just wondering.. :)


Is it the chemical makeup, molecule size, or just hair type that changes the length of time it stays in?Why does red hair dye fade in a few weeks, brown come out over time, and black dye not fade at all?
Red is a mid range color, Most effected by light. UV light in particular. All red color fades over time. In sunlight.