Fill a large glass with ice.

In a separate glass add sprite and 1 drop of food coloring mix well.

In glass #2 add 1/4 cup of Pina colada mix and 1 drop of purple food coloring.

 Pour sprite mixture into the glass filled with ice ONLY; fill 2/3 of the way full.

Now add the Pina Colada mixture pouring it down the side of the glass. It will work its way to the bottom since it's a heavier liquid than sprite.