guess my reply is probably a little late, but here it is anyway- I learned 2 different "recipes":
1st I learned from some Indian women in Cali and they mixed henna w/ black tea/coffee, cloves, a few drops of eucalyptus oil mixed into a paste. After applied, dab a mixture of lemon juice & sugar a few times and let set as long as possible. *scrape the paste off, not washed w/ soap & water til later.
2nd in Maroc, the lady who did my engagement henna mixed the henna only w/ water and then dabbed the lemon juice and sugar mixture also. I slept w/ that on and scraped off the next morning, then gently washed, not scrubbed the area.
*Everytime I've had henna done it darkens over the next 2 days. Personally, I've had both the black & the reddish/orangish/brown henna and I just prefer the latter... it usually turns such a nice color and I'm pale also. The black totally looked like a sharpie!

I just got a fresh supply of henna this week from Maroc - my sweetie sent me a care pkg! The fresher the henna, the longer it will last on the skin and the darker it will get.
Good luck![attachmentid=2446]