boil 4 big, previously washed, leeks in a litre of water for 20 minutes. Use this water as last rinse after your shampoo.
For blondes this recipe will accentuate the golden strains in their hair with the same method but with two handful of German Camomile flowers instead of the leeks.
Picture just to illustrate not actual result.
Both could use the following recipe to get reddish highlights in their hair by rinsing with water from a litre of water in which tea and onion peels have cooked.