Whip egg whites and castor sugar till soft peak.
Add sieved almond powder and icing sugar.
Fold in with a spatula.
Add a drop of gel colouring.
Pipe on paper with the shape drawn on the underside.. Bang the tray several times to release air bubbles. Leave the tray till the piped macraons are no longer tacky when lightly touched. Bake at 150 C for around 15 minutes. Let them cool thoroughly. Sandwich them with ganache or any filling of your choice.