Soak gelatin in cold water for about 10 to 15 minutes. Add food color if desired.
Place warm water in a saucepan and add the sugar previously mixed with gum arabic. Heat and stir until the sugar is dissolved. Do not boil.
Add the soaked gelatin and stir until it is dissolved.
Add the corn syrup and heat the batch until stiff and fluffy. Add calamansi oil.
Place the mixture in a plastic bag which has an open end at the side. Squeeze the bag to release a circular form marshmallow passing through the open end. Cut into desired sizes. This can also be done in a marshmallow molder.
Cast the marshmallows into starch (containing not more than 8% moisture and previously heated to 32-35°C.
Place trays containing the starch and marshmallows (previously starch-casted) under room temperature for 10 to 20 hours.
After a slight crust has formed on the marshmallows, remove from the starch. If to be packed plain, dust with a combination of dry powdered sugar and dry starch.
Let remain covered with the starch-sugar mixture for several hours before packing.