Combine agar-agar powder with 120ml water. Stir to dissolve, then pour into the hot water.
Add sugar and screwpine leaves and bring to a boil for 10-15 minutes over a medium heat. Stir occasionally while cooking.
Divide agar-agar into three portions. Add colouring to the two-thirds portion and pour into wet moulds.
Bring the remaining one-thirds liquid to a gentle simmer, then add thick coconut milk. When it begins to boil, remove from the heat at once.
Test the doneness of the coloured portion. It should be about set. Gently pour spoonfuls of coconut milk agar-agar mixture over the coloured jelly(take care not to break through the surface of the coloured jelly).
Leave to set completely. Chill in the refrigerator before turning out.
Should the coloured jelly set before the coconut milk agar is being added, you can scratch the surface with a fork before pouring in the topping.