To prepare filling: Steam the beans together with the pandan leaves for 25-30 minutes over high heat. Discard the pandan leaves.
Process mung beans with sugar, salt, shallot oil and candied melon to a smooth paste. Divide equally and shape into balls.
To prepare skin: Steam sweet potatoes until tender. Mash into a smooth paste while hot and combine with glutinous rice flour, wheat starch, sugar, and oil. Add coconut milk and water. Knead until smooth and divide into two portions.
To one, add orange colouring and mix well. Divide into equal portions.
To the other, add green colouring and mix well. Divide into equal portions.
To wrap and shape: Flatten a piece of dough and place a filling ball in the centre. Wrap dough around the filling and shape into a ball. Press it into a dumpling mould. Knock out the dumpling and place on a small square of greased banana leaf.
To steam: Steam over high heat for 7 minutes, or until cooked. Remove and brush lightly with oil.