Before applying on your hair you may add jojoba or burdock oil to henna powder dissolved in boiling water. It leads to double effect: a dye covers your hair evenly thanks to oils; at the same time it strengthens the hair roots. Also, in order to achieve the synergies you may dissolve henna not with boiling water but with hot whey, which would make your hair shine and smoothness.
Vegetable oil can also neutralize the excessive color brightness. You should warm up a bit of vegetable oil (preferably on a steam bath) and rub it into dyed hair carefully. Wait until your hair becomes dry, and wash it with shampoo. Repeat the procedure if the result is not noticeable.
Henna is used to fade. But do not use henna more often than once in a period of two months. You could get a reverse effect from frequent use of henna: your hair may become dull. If you want to refresh a dyeing, do it using henna rinse. Dissolve 1 package of henna in 1L of boiling water (you can change the proportions, depending on hair length). Filter the mixture carefully; then cool it and rinse your hair with it.
You can get almost all most fashionable hues from flame-red to bright brown using henna. If you want to have got a deep chestnut color on dark hair, add 1-2 tablespoons of instant coffee.
And if you prefer colors of bordeaux, dissolve henna powder in hot beetroot juice but not in water. Henna also can help you to become a brunette: mix henna with basma in equal proportions to rich this effect. Basma is a dyeing powder extracted from leaves of indigo.
To achieve more interesting colors mix henna powder with such decoctions. Chamomile decoction (chamomile gives hair a wonderful golden hue) lime flowers decoction (you will get brown hue), onion skin decoction (a warm color of brown or purple, if onion is blue), buckthorn, calendula, tansy decoctions (you’ll get yellowish color options), or juice of elder-berries decoction (violet-red, purple colors) or raspberry decoction (red hues).