Preheat oven to 325°F. Mix flour and salt in large bowl. Set aside. Beat butter and sugar in large bowl with electric mixer on medium speed until light and fluffy. Add egg and vanilla; mix well. Gradually beat in flour mixture on low speed until well mixed.
Roll out dough on generously floured surface to 1/4-inch thickness. Cut out hearts with 3-inch heart-shaped cookie cutters. Place on ungreased baking sheets.
Bake 8 to 10 minutes or until edges start to brown. Cool on baking sheets 1 minute. Remove to wire racks; cool completely.
Spoon frosting into medium microwavable bowl. Microwave on HIGH 20 to 30 seconds, stirring every 10 seconds. (Frosting should be a pourable consistency.) Dip tops of cookies into frosting. Place frosted cookies on wire rack set over foil-covered baking sheet. (The baking sheet will catch drips.) Let stand 10 minutes or until frosting is dried.
Prepare 3 colors of Flavor Paints (see below). Paint stripes of red then medium pink then light pink on each cookie, cleaning paint brush in between colors. Let stand until paint is dried.
Red: 1 teaspoon McCormick® Pure Vanilla Extract and 1/2 teaspoon McCormick® Red Food Color
Medium Pink: 1 teaspoon McCormick® Pure Vanilla Extract and 10 drops McCormick® Red Food Color
Light Pink: 1 teaspoon McCormick® Pure Vanilla Extract and 4 drops McCormick® Red Food Color
For Ombre Design: Paint stripes of red then medium pink then light pink on each cookie, cleaning paint brush in between colors.