Perhaps Pink


1 oz Rhubarb Liqueur
1/4 oz Simple Syrup (cardamon is good)
1/4 oz lemon juice

Shake over ice.  Strain and top with grapefruit soda, we like to use the Pelligrino Pomelo.  Garnish with candied rhubarb slice if you feel like fussing, or a curl of lemon peel.