In a small saucepan, combine the honey and lime juice.
Bring to a boil over medium heat. Add the mint leaves and remove from the heat.
Steep the honey mixture for 5 minutes, then pass the mixture through a fine-mesh sieve placed over a bowl, pressing down lightly on the leaves with the back of a wooden spoon.
Refrigerate the syrup until cold.
In a large pitcher, combine the mint syrup, grapefruit and orange juices, and lime zest. Stir until the syrup is dissolved.
Pour into tall, chilled glasses and garnish each glass with a lime slice.