Meanwhile, in medium microwavable bowl, microwave 1 cup of the white vanilla baking chips uncovered on High 45 seconds. Stir; if necessary, microwave in 15-second increments, stirring after each, until chips can be stirred smooth. Cool 5 minutes. Stir in frosting until well blended. Reserve 2 tablespoons of the frosting mixture to attach decorations. Use gel food colors to tint remaining frosting in desired colors. Spoon each color of frosting into resealable food-storage plastic bag. Cut 1/2 inch off one corner of bag, and pipe on bottom of 1 cookie. Press another cookie, flat side down, on frosting at an angle, cookies touching on one side and about 1 inch apart on the other, to look like open mouth.