It's popular for both temporary tattoos and hair color, and it makes a gentle alternative to henna or indigo. So if you're looking for lush black hair color without chemical dyes, pop by your specialty grocery and see if they have any huito. If you can't find the fruit but want to try the dye anyway, you can also buy huito extract (it's sometimes also called jagua) in many health food stores.
Huito is the natural equivalent of bacon cupcakes: an unexpected combination that really hits the spot for some people. The yummy fruit, which grows across the Caribbean and all the way down to Peru, makes both great jam and a pretty awesome black hair dye. When ripe, it's popular as a flavor for preserves and ice cream, but when it's still green the geniposidic acid it contains makes a tenacious dye when it oxidizes, dyeing anything it touches a rich blue-black.