I couldn't really say, but they would dye it by washing it in lime.
They used to do this naturally by washing it in lime and combing it back.
Have you ever colored your hair? I made mine purple once as a kid! That's interesting! The main reasons people dye their hair is to cover gray or to make it seem more fashionable, or just to restore the original color. Yeah, I did it just to make it look neat! Coloring hair can be done by a professional or at home, was yours done at home? Yeah, I was just a kid doing something dumb. I messed mine up royally as a kid, it is worth the investment for a professional! Celtic people used to dye their hair blonde. is that right? that is interesitng, I wonder why!
Their hair is blond, but not naturally so: they bleach it, to this day, artificially, washing it in lime and combing it back from their foreheads.