Henna
Mix enough powder with 200 ml cooking water to a not to thick paste. Add a teaspoon of lemon juice and let paste cool down to a pleasant temperature. If your hair is very dry you may add an egg. Apply paste on your hair and let it work as long as you want (from half an our to a night).
To make your hair darker
Mix juice of one lemon with a cup of strong coffee and rinse your hair without washing out.
For brown hair
Walnut oil applied with cotton-wool swab is helpful to get your hair darker. But attention it may cause spots.
To make blond hair brighter
Make a tea from 2 teaspoons dryed camomille blossoms and 600 ml cooking water and rinse your hair. You may dry it at the sun.

E.

When I was using henna on my hair, I used to mix it up with a little red wine vinegar for the acid (to help intensify, like the lemon juice does) and for its scent. It really helped draw out the color, and cut down on that 'fresh dirt' aroma. ;)

And remember to clean up the room you're applying the henna in immediately and /thoroughly/ after you've got the henna in your hair! My bathroom has a few stains in the wallpaper from where I missed tiny splotches of the henna the first time I went over the room, and didn't find them until they had dried thoroughly. :/

Rinse with water until the water runs clear. It takes -forever- to get it all out. If your hair is dry, I'd condition afterwards, but not shampoo.

You could try dyeing the gray to your natural color first, and then dyeing the whole of your head. Beware though, dye makes your hair very dry, are you sure you want to do it? Also, you could just leave the gray streak in and dye the rest if you're worried about the color.

One natural method for blonde hair I have been using is a rinse/leave-on treatment with rhubarb root.I mix pulverized rhubarb root with boiling water,let it cool off a bit and then apply it to the hair for about 45 mins.This has always given nice golden highlights to my dark blonde hair,but it is VERY messy(stains!)and I never liked the smell.So I hanven´t been doing this for a while.
Anne-Marie

I used only about a handful,in Germany you can buy it in pharmacies/healthstores,it comes in small pieces(not as a whole root).I put them in a coffee grinder to get a fine powder.
Anne-Marie

Hm,I´m not sure.Maybe you could leave the root to dry for a few days after digging it out?It might be hard to pulverize it otherwise!I never thought about digging out the root actually we´ve got one  plant in our garden too.I hope you like the colour effect,it has always given me very golden highlights.

Well - one thing I would definitely make sure not to do for enhancing blonde hair is to use lemon juice (whether squeezed fresh or from extract) it will dry out your hair, and leave it susceptible to damage - especially if you use either heat instruments on your hair or in the summertime when out in the sun or in chlorine - it's awful!  I've seen what it's done to other friends of mine hair, and it's not worth it!  In winter time (when my hair sometimes looks darker since it gets a lot lighter in the summertime) I just use a spray of sun-in (not natural I know, but it's gentle on my hair, and has leave-in conditioners) whenever I need to blow-dry my hair a bit so that it doesn't freeze when leaving the house!