Combine butter, granulated sugar, brown sugar and egg yolk in med. bowl. Add flour, baking powder and salt; mix well. Cover; refrigerate until firm, about 4 hr. or overnight. Roll dough on floured surface to 1/4 in. thickness. Cut into oblong candy corn shapes. Place on ungreased cookie sheets. Preheat oven to 350 degrees.Bake 8 - 10 min. or until edges are lightly browned. Remove to wire racks to cool completely. Glaze: Combine 4 cups powdered sugar and 4 tbs. milk in sm. bowl.Add 1 - 2 tbs. more milk as needed to make med.-thick, pourable glaze. Divide Cookie Glaze into thirds; place in separate sm. bowls. Color 1/3 glaze with yellow food color and 1/3 with orange food color. Leave remaining glaze white. Spoon glazes over cookies to resemble candy corn. Let stand until glaze is set.