After much research, I have found a black ink that is safe, and produces the black color people ask for, and lasts for the same amount of time as henna. The indians of the rain forests of Central America for years have been using a extract of the Genipa Americana fruit to produce their tribal tattoos. It has been used for over 12,000 years for medicinal purposes, and traditional body art in Central America. Unlike many temporary tattoo inks on the market, the ink gel is easy to see on dark skin.
The regular strength gel lasts from 10-14 days. The extra strength gel lasts from 15-20 days. Both all natural temporary tattoo ink gels disappear as your skin naturally exfoliates. The time frame is defined as the originating image time until the image is fully faded from your skin. Washing the area more than once daily will significantly decrease the time frame for the gels.
The blue/black color will appear fully within 12-24 hours after the application process. Application is done in the same process as henna. The ink takes about 45 min to dry, and is recommended to leave on the skin for about 2 hours, then the ink itself is peeled off. Once peeled, you may see nothing, or you may see a light gray color. But in about 12 hours, you will have a black design.
This ink / gel has only recently been introduced to the rest of the world as an addition to henna body art. This black ink is also used by those thinking of getting permanent tattoos, to see if it is something they really like and are ready to commit too.