Beat the egg whites until stiff, then slowly add in the sugar. Beat continuously until the egg whites are satiny and smooth.
Then, add corn flour, vinegar, orange rind, and the colouring. Continue beating till well combined.
Next, on a greased tray or a tray lined with a silicon sheet, drop ½ teaspoon of the mixture onto the tray and leave a 1 inch gap between cookies.
Bake in a preheated oven at 130°C for 45 minutes.
Let it cool and store in airtight containers.