You might associate it with college-era bar-hopping, but blue curaçao is actually more than 100 years old. Its orange flavor plays nicely with lemonade in this citrusy slushie.
Combine all ingredients, except garnish, in a quart-size zip-top bag. Seal bag and freeze overnight. To serve, massage the bag to break up mixture. Tip slushie into a glass. Add garnish and serve immediately.
Make a bigger batch in a gallon-size zip-top bag for serving at a party.