Henna is normally very time consuming and messy. From what I've read, if you are getting anything other than red from it, it isn't pure henna. Henna is wonderfully conditioning though, so it may be an option... but read up on it first:
www.hennaforhair.com
You can also do a Henna Gloss which is much more subtle, or a Henna/Indigo Gloss which supposedly gives your grays a nice blond color and the rest of your hair a richer brown. (Do a search for info about that at hennaforhair.com.)
It's important to make sure you use pure, body-art-quality henna on your hair though, which you can read about and purchase at the link above.
Another easier and more subtle option is to use Cassia Obovata - commonly referred to as neutral or colorless henna - to give your grays a more golden hue. I use it along with Chamomile tea and I love it. It makes my grays golden and my light brown hair look richer and healthier.
If you would like to use non-toxic haircolor, you could try Natracolor which gets mostly incredible rave reviews on MakeupAlley.com:
http://www.makeupalley.com/product/s...and/Hair_Color
Or Eco Colors from
www.Ecocolors.net You may even find a local salon that uses EcoColors. There is an area code search for salons on that site.
HTH.
