Heat oven to 350. Spray 24 regular size muffin cups with cooking spray. In medium bowl, mix brownie mix, oil, water and eggs. Divide batter among muffin cups. Bake 13 to 18 min. or until centers are set and toothpick inserted near edge of cupcake comes out clean. Cool 30 min. Run metal spatula around edge of each brownie, lift out to remove from muffin cup. In microwavable bowl, microwave vanilla chips uncovered on med. 30 to 45 sec. stirring every 15 sec. until melted. Cool slightly. In medium bowl, beat powdered sugar, butter, milk and food colors on med. speed until fluffy. Stir in melted vanilla chips. Spoon frosting over cooled cupcakes, top each with candy bar.