Henna Help . . . . . . . . .?

I've never heard of that before. I know that if you add a couple drops of olive oil it's supposed to brighten the color. I have pure red, and pure black henna, and I use them for tattoos and they look pretty nice. For me, (I have them on my feet and chest) they've lasted a few months. I had them on my hands, but with my frequent washing that I do, they usually rub off pretty quick, within a few days. I'll look into it some more, and come back and edit this answer.

***EDIT***

It turns out that you can. Here's a list of things to do from a FAQ list on a Henna website.

"The following formulas work best:

Medium Brown - Henna + brewed coffee + apple cider vinegar

Dark Brown - Henna + brewed coffee + apple cider vinegar

Light Brown - Henna + Ceylon or Black China Tea + apple cider vinegar

I do not recommend adding olive oil, yogurt or egg to henna when trying to cover gray hair. It seems to interfere with the henna's ability to stick to the gray."

***EDIT AGAIN***

Thank you so much for that download! I loved reading it. I appreciate it!

Any acidic liquid will help break down the leaf and release the dye, but there's lots of things that will smell better than vinegar. Lemon juice, tea, or OJ for example.