To prepare this recipe, combine all the ingredients in a large bowl and mix (with a hand mixer or a stand mixer) on low speed until blended. Increase to medium speed and beat until the icing holds thick, soft peaks, 4 to 6 minutes. Test the icing for outline consistency by piping a small amount through a decorative tip. If it tends to curl back or is difficult to pipe out, the icing is too dry and needs a few drops of water. Conversely, if the piped icing seems runny, add confectioners’ sugar, a tablespoon at a time, beating on low speed to blend. Don’t overbeat or the icing will stiffen and lose its gloss. Divide the icing among clean containers, one for each color to be used. Tint as desired with concentrated food coloring pastes or powders (liquid colors can thin the icing too much). Add each color by dipping a toothpick into the paste and transferring small amounts to the icing; stir with a spoon until no streaks remain. Keep the containers sealed when not using them.