Sorry, I didn't see this until now to reply!
i really prefer the henna for my hair. i get amazing color and shine and no sore spots on my head.
however, i don't follow the package instructions. i instead follow instructions i have found on a henna for hair website.
the henna takes time to *release* dye before putting on hair. depending on the temp and what else is in the mixture that can take a few hours or 24 hours. i like to mix my henna with 2 cups of camomile tea, 1/4 cup apple cider vinegar and enough water to blend. then i let it sit covered in a warm place for about 2 hours, or until the dye has released.
you will know when it has released when the top of the mix is a dark chocolate brown and scraping that off reveals a bright green gloppy mess.
i put the whole thing on my hair, trying very hard not to get on my skin and leave on anywhere from 2-6 hours. i keep it covered in plastic so that my head stays nice and warm.
then off to the shower to rinse, rinse and rinse again! i try not to wash for about 24 hours.
i have really rich color doing this, which deepens and brightens to the final color about 2 days after hennaing.
everyone does thier own henna differently and i have seen some really elaborate receipes. all you really need is the henna, water and something acidic (vinegar, citrus, etc) to start the dye release.
hope that helps