Giffard Watermelon liqueur is a pale, pink color and part of their classic liqueur line. They say it comes from a Spanish melon infusion with a slightly acidic finish.
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.