Prepare a tall glass full of ice then add the White Grapefruit juice (has to be White, not RubyRed, or else the Neopolitan effect will not occur). Next add the Grenadine and watch as it passes through the juice and sinks to the bottom of the glass. Finally, add the Light rum; it should sit on top of the grapefruit juice. DO NOT MIX. Let the glass sit for 3 minutes and watch as the middle layer (grapefruit juice) turns very light brown. You now have the Neopolitan effect (red, brown, white) and a very tasty drink. Enjoy!