Zakkalife blog says: This key cover was made from a small water balloon. The idea came to me when I saw a bunch of broken balloons lying on the ground. Something about them reminded me of key covers. So here’s an easy inexpensive way to color code your keys. Simple directions below.
Take a small water balloon and cut it in half. Place the top part over the key. Trim back any excess balloon with a pair of scissors. Poke a hole with a toothpick through the part of the key that hangs on the key chain. Done.
Do It And How 