When ordinary ice just won't do, it's that 70's ice! (not responsible for strangely discolored drinks) I have done this WITHOUT food coloring, to make oddly mis-shaped ice, which looks very un-usual in the freezer. (mom hated it!)

You need:
ice cube tray, freezer, and water
food coloring (optional)

Step 1: First Color

For the first layer (yellow), only fill each cubicle halfway up, then freeze. When frozen, remove the ice and carefully stand each cube up, the long way, in it's cubicle. (Added 9/29/2011 Don't use straight food color! Use a dilute solution, 5 or 6 drops of color in a half cup of water. dreamberry)

Step 2: Green

With the first cubes standing upright, carefully fill each cubicle with the second layer of water (green) and freeze.

Step 3: Red!

Now remove the ice and stand the cubes up again, perch or wedge them as you may need to, so long as some of the next water will freeze to them. Carefully refill the tray with more water (red) and freeze.