In a medium saucepan, combine the sugar and gelatin. Stir in 2 cups of the orange juice. Cook and stir until the sugar and gelatin dissolve. Remove from heat. Stir in the remaining orange juice, the orange zest (or oil), milk and a few drops of orange food coloring.
Transfer the mixture to the frozen ice cream maker container. Process according to your maker's instructions.
Transfer the sherbet to another container, and freeze at least 4 hours before scooping and serving.