Place sago in a bowl. Add green food colouring and pour in water. Allow to soak overnight in the refrigerator.
Combine grated coconut, castor sugar, soft brown sugar and salt in a mixing bowl. Bring water to boil. Add well-drained sago. Cook and stir vigorously until transparent. Strain sago into a metal sieve and washing under running tap water to remove excess starch. Drain well and add to the grated coconut mixture. Mix evenly.
Spoon mixture into prepared pandan leaf casing. Arrange the pieces in a steamer and steam over high heat for eight to 10 minutes.
To prepare the casings: Cut each piece of pandan leaf into 17.5cm lengths. Fold into five equal parts at 3.5cm intervals. Snip each of the first four parts up to the centre, i.e. nearest to the vein of the pandan leaf. Make a case by folding the leaf following the cuts. When you come to the last part, fold it in and staple up to hold.