Produces more intense multiple colors because it is done with straight icing color brushed into the bag. Apply one or more stripes of icing color with a decorating brush, then fill the bag with white or pastel-colored icing. As the icing is squeezed past the color, your decorations will come out striped.
Consider the type of icing you are using when mixing color. Icing colors intensify or darken in buttercream icing about 1-2 hours after mixing. Royal icing requires more color than buttercream icing to achieve the same color intensity.