Giffard Blue Curacao (or Curacao Bleu, as they would have it) is made with a combination of bitter and sweet oranges along with the striking, sapphire blue that can be so exciting in cocktails. The name is an homage to the Caribbean origins of this style of spirit.
Giffard is a French company specializing in a wide variety of liqueurs and eua-de-vie among other products. Some of those extra products are flavored cocktail syrups (or "sirop"). They are generally sweetened with pure cane sugar.