Use paste or gel food coloring to make bright blue frosting that you can easily spread or pipe from a pastry bag to make decorations. These concentrated food coloring varieties will not thin the icing. The amount of liquid food coloring required to achieve the same bright blue color would significantly thin your frosting, affecting your ability to spread the frosting over cake or pipe rosettes or other decorations.

Paste and gel food coloring produce very vivid colors with just a small amount. You can get the shade of blue illustrated on the package through careful mixing and adjustment. If your desired color is slightly darker than the lighter blue food coloring hues available, use one part royal or navy blue to one part sky blue in your frosting. If you’re using your bright blue frosting to make a water-themed cake, you may want a shade of aqua blue. Use equal parts light blue and medium green to make bright aqua blue frosting.

Scoop a small drop of paste food coloring onto the end of a toothpick and add it to your uncolored frosting, or squeeze in one drop of gel coloring. If you’re working with more than a couple of cups of frosting, mix with an electric mixer; otherwise, you can just stir the coloring in. If the color is not deep enough, add one more drop of coloring and mix again. Stop adding color when the frosting is a few shades lighter than you desire. Cover and let the frosting rest for a couple of hours.

If the frosting is too dark, mix in a drop or two of white food coloring to lighten it. White food coloring is available wherever baking supplies are sold. Typically used to remove the yellow hue from buttercream frosting, it is available in paste or gel, neither of which will thin your icing. Once you are satisfied with the color, decorate your cake, cupcakes or cookies with the frosting.