Grenadine

Grenadine (grenadine syrup) is a blood-red, strong syrup made from pomegranates. It is the number one among fruit syrups, and is used in many cocktails not only for sweetening, but also to give them a red color.

Grenadine syrup for use in a bar is usually bought on bottles, but you can also make your own:
Use 4 pomegranates to make about 2 cups of pomegranate syrup. After removing seeds, process with food processor knife blade. Simmer pulp with 1/4 cup honey over low heat 3 minutes. Stir well. Strain to remove seeds.