Turning your skin from white to black is easy as long as you have the right equipment. Usually, this involves some sort of make-up that can penetrate and cover the skin well. They are several forms of make-up to choose from, but most performers (clowns and actors) use grease make-up.
Obtain a package of grease make-up. You can purchase it in a costume store or online. Both sources for this product are good. However, as with many items, you can find a bigger variety of it on the Internet. Be sure to pick out the right color. You will see a range from light mocha to ebony.
Remove any item covering the skin you want to color black. This process will mean pinning back hair or taking off clothing. You need to be able to apply the grease make-up without any obstruction.
Cleanse your skin. Use water and your normal cleanser. Be sure to rinse and dry your skin afterward. You want to have a clean palate.
Apply the grease make-up. Use a make-up sponge to put it on. With even strokes and pressure, apply it over the different sections of the skin you want to turn black. Take your time, so you don't end up with any white showing through the grease make-up.
Set your grease make-up with powder. You can get it at the costume store. Be sure that it is the same or very similar color as your grease make-up. If not, it will make your skin look blotchy and spotty.