1.Combine sugar and water in a medium saucepan. Stir over low heat until sugar dissolves, brushing down sides of pan with a wet pastry brush. Add rind and bring to the boil. Boil, without stirring, for 3 minutes. Pour syrup into a large heatproof jug.
2.Add juice and a few drops of green food colouring to the syrup; stir until combined. Pour syrup through a fine sieve into hot, sterilised glass bottles. Discard solids. Seal; cool syrup to room temperature.