Easy! No egg whites or piping bags needed :) AND it tastes so good! Double or Triple if needed, especially if you will be dipping the cookies.
4 T powdered sugar
1/2 T water
1-2 drops food coloring
small dish and paint brush or large shallow dish for dipping
Stir in a small bowl until completely smooth, add drop or two of additional water if needed. Paint onto cookies or dip cookies. Should be thick enough for a layer and not run off or soak in, but thin enough to flood itself. Adjust with a drop of water or teaspoon of powdered sugar if needed.