Preheat the oven to 180 degrees C. Line a cupcake tin with patty cups.
Sift the flour, baking powder and salt together three times. This gives a lighter texture.
In a separate bowl, beat the egg whites until frothy. Add 100g sugar and continue beating until soft peaks form.
Cream the butter until smooth. Add remaining sugar and cream until light and fluffy. Add the flour alternately with the milk in small amounts, beating well after each addition. Add vanilla and mix in egg whites.
Place a little of each food colouring in six different bowls with a different colour in each bowl. Divide the batter evenly between the bowls and stir until each is a uniform colour.
Place a tablespoon of the first colour in each patty cup and smooth out to the edges. Repeat with remaining colours.
Bake 20 minutes, or until a skewer inserted into a cupcake tests done. Cool slightly in the tin then remove to a wire rack to cool completely. Ice with your favourite icing, or enjoy plain!