You'll need about 3/4 cup of lemonade per 2 cups of ice, per color. This will allow you to layer the 2 glasses as shown. I used the following color combinations:

• For green lemonade, use neon green and 1 drop of regular green.
  Neon green food coloring, green food coloring, 1 pitcher lemonade
• For blue lemonade use neon blue.
  neon blue food coloring
• For purple/violet lemonade use neon purple and 1 drop regular blue.
  neon purple food coloring, blue food coloring
• Add lemonade to a measuring cup and color with food coloring. Stir well. Add 2 cups of ice to a blender and pour in 3/4 cup of lemonade. Blend until a slush is formed. Spoon slush into the glass, filling it 1/3 full.
  ice
• Repeat for each color, layering it into the glass in color order desired. Serve immediately.