Freeze for a few hours (or overnight if you have time)
Mix in food processor (DO NOT use hand mixers or they will break!!!)
Refreeze and pour into a 9x13 pan if you want to layer, or into a freezable bowl if scooping like ice cream
Repeat with different colors and layer as each color sets if you want a rainbow effect. You can also experiment with different juice flavors (I've used apple juice, grape juice, raspberry, mango - anything interesting to change it up a bit)