Fuck it I'll just post it anyway.
You need to get a stick of beeswax. I don't know where to get it here in the states, because Georgia doesn't have any useful non-chain stores, but I think if you can't get it in stick form places that cater to African hair types might have some (and salons might have the pure stuff). If you get the stick, break off a little chunk and roll it around in your hands until it is soft and warm, and then smear it evenly on your skin. It makes the actual pigment stay even and clean without cracking, and it comes off with makeup remover, so don't worry about it clogging your pores or whatever since you will probably only have it on for a few hours.
White theatrical foundation makeup is next. If I recall correctly from my Swan Lake days, you can get this for really pretty cheap at Sally's Beauty Supply or even CVS pharmacy (or Boots maybe, for the UK, but not sure). This is good, because you have to shatter it. This is easily done by closing the compact and dropping it on the floor or banging it against the countertop. Open the compact carefully and dump the shattered pieces into a bowl and add water until you get to a texture just thinner than a paste. Stir this up reall well and make sure all the chunks of foundation powder are dissolved. Apply using a makeup sponge, or preferably a big poofy makeup brush (the cheap kinds with synthetic bristles are actually a little better for this because the bristles are a little stiffer). Depending on what ingredients your particular brand uses, you can use talcum powder or corn starch (I think you can, anyway) for adjusting the colour and consistency and opacity. However, I have no experience with this so you will have to play with it yourself.
Of course, you can skip all of those difficult steps with the mixing and jump right in with a wet makeup sponge on the dry (intact) compressed powder in the compact, but trust me when I say that the mixing gives you a better result and (depending on how much surface area you are covering) is arguably faster. DO NOT try to substitute eyeshadow for this part, because the little shimmers of Red #40 or whatever it is will fuck it up. I actually don't know the chemistry behind this, but it doesn't work. One standard-size compact (about palm-sized, I guess?) should actually enough to cover pretty much your whole body this way, if you want; we did this for Swan Lake costumes on arms, backs, chests, faces, and necks, and usually a compact could finish three to four people.
Anyway, you need a dry and rather porous sponge on hand to blot off the extra makeup. By this I mean that you should have slopped it on and your skin should look, feel, and be very wet with makeup when you put it on, but not to the point of dripping. I know it feels like you are wasting a lot when you blot it dry, but you really aren't. I found some yellow craft sponges once that worked really well, but I have never been able to find them again so I don't know what kind they were or anything.
Last step is finishing powder. It really doesn't matter what kind you use, but it needs to be loose. If you already have something in mind (say eyeshadow) to use and it's compressed, you can try shattering this too and it should work. Otherwise, I recommend a really cool thing I happened to stumble upon in Sally Beauty Supply one day [looking for a new Super-Comb for my ridiculous hair] that was a translucent rice powder finisher, and it goes on great over any colour at all.
This shit will stay all day. It will last far beyond the sweat and heat of bodies in one of the longest and most intensive ballet productions ever with no need for touch-ups or reapplications, so it should work for whatever you want, although I don't know if it will hold up in rain. The wax keeps the makeup from smudging, smearing, sweating off, running, or anything and it looks pristine. Plus, as long as you don't leave it on long enough to clog your pores, beeswax has got some enzyme shit in it that is good for your skin, so you might even benefit from it longer term, which is always cool.
