This is how the young green (or Thai, as they are sometimes referred to) cocnuts look when you get them. The green husk has been chopped away.



This is what it looks like after you puncture it to drain the liquid, and cut it open.
It should be nice and white. If it's pink, purple, or grey, it's spoiled and you
 should throw it out.

These can be purchased at healthfood or natural food stores, and asian markets, as well as a few other ethnic markets. If your local organic food store doesn't carry them, ask. My market started, and once we told them we would like more, they started getting them in weekly. They cost $1.99 where I buy them, but some people are getting them for under a dollar apiece. They are worth it.