In a small bowl, mix 1/2 cup water with red food coloring until you achieve a vibrant red. Place a slice of strawberry in each compartment of an ice cube tray. Pour the red water over the strawberries, filling each compartment about one-third full. Freeze for 15 minutes until solid.
In another bowl, stir 1/2 cup water with sugar (if using) until dissolved. Once the red layer is frozen, remove the tray and pour the white water over the red layer, filling each compartment another third. Freeze again for 15 minutes.
Mix the remaining 1/2 cup water with blue food coloring. After the white layer is set, pour the blue water over it, filling each compartment to the top. Add a blueberry to each cube if desired. Freeze for at least 30 minutes or until completely solid.
Remove the ice cubes from the tray by twisting gently or running the bottom under warm water for a few seconds. Drop 2-3 cubes into each tall clear glass, add your favorite clear beverage (lemonade, soda, or water), and garnish with a striped straw.