Curaçao is a type of orange liqueur invented on the eponymous Caribbean island of in the 19th century by the Senior family. Curaçao utilizes the native laraha, an adapted version of the Spanish Valencia orange that was brought to the island in the 16th century. The laraha is green and inedible, but the peels have a wonderful aroma of bittersweet oranges.
Curaçao comes in many different colors: clear, orange, blue, and green being the most predominant. The clear version is quite suitable for substitution for neutral spirit based orange liqueurs in cocktails, and is the normal color of the liqueur -- the others are artificially colored.
The Senior brand is called "Curaçao of Curaçao" in order to differentiate it from other producers not on the island like Bols or Hiram Walker.