After I discovered Lush products,
link to their sites, I started using their Henna Hair Dyes. I use their Caca Rouge Henna and I find it leaves a nice, natural looking reddish tinge to my hair. And the blonde bits of my hair turned a nice strawberry blond.
You can read all about their henna's here and even see what ingredients they use as well.
http://www.lush.ca/shop/products/haircare/henna-hair-dyes/
(Using the Canadian English site since that's where I am.)
Now mind you if you wanted to do a darker colour like brun or noir you would need to do the rouge first since it wont stick to your hair, especially if you have grey/silver hair like I do.
Now this is not the most pleasent smell out there, but the effects are worth it. The bricks of henna come in small blocks of 6. Now if you have short hair like I do, (reaches your shoulders) and if it's thin like mine, you'll only need 3 of those blocks to dye your hair with. If it is thicker or longer you will need more. Possibly even 2 bricks of the henna if you have super long hair or it's especially thick. Now you can dye your hair with this as many times as you want right after each other without it harming your hair because of all the cocoa butter they use as their base.
Now if you don't like the colour after leaving it in for a day, (because the colour intensifies after a few hours and deeps as it dries), they have some hair products that can wash it out with out harming your hair. I was told H'Suan Wen Hua Hair Treatment was their best to use should you ever dislike it.
Now if you want long lasting colour with these bars they say to leave it in for 3 hours. I do 6. I dyed my hair last August and haven't had to since. A root touch up should only take 1-2 blocks of the brick at the most.
Any more info you want to know just ask. ♥