For the icing, sift the powdered sugar and mix into the egg white. Remove 4 tablespoons of this glaze and tint with yellow food coloring. Put the yellow glaze into a freezer bag and set aside. Coat the cake with the white glaze and let dry. Then, cut off the tip of one of the corners of the freezer bag to use for piping the yellow glaze. Pipe thick lines of the yellow glaze to look like yellow petals. While the glaze is still wet, decorate with sugar flowers.