Grapefruit liqueurs come in an impressive variety of colors and sweetness levels. We prefer the pink stuff for lovely color it adds to our drinks, but you can find fine examples in red, orange, yellow, and even clear.
Grapefruit liqueur is easy to DIY, too. Peel a few grapefruits (taking care to avoid the bitter white pith), soak the peels in vodka or another neutral spirit for about a month, and mix the infused spirit with as much simple syrup as you like.