In a bowl, mix the icing sugar with the water, adding a little at a time. You want a just pour-able consistency. Add the yellow food colouring to create your desired stage. Gel food colouring is preferable but just watch the consistency of your icing if you are using a different kind of food colouring.
Starting with just a teaspoon, pour a little icing on top of the cream. After it has started to run down the cream, you can see where more is required and simply pour a little more into these places.
Allow the icing to set before serving.