In the bowl of an electric mixer, beat the egg whites on low speed until just frothy, about 1 minute. Beat in one-fourth cup sugar. Add the remaining sugar and beat on high speed until the mixture holds a peak and is very thick, 5 to 10 minutes. To keep a crust from forming, cover the icing with a damp towel. If the icing needs to be thinned, add a little water. Add food coloring as desired.