For the Cupcakes, prepare cake mix as directed on package, adding vanilla. Spoon into 18 paper-lined muffin cups.
Bake as directed on package for cupcakes. Cool cupcakes on wire rack.
For the Unicorn Twist Frosting, beat butter and vanilla in large bowl until light and fluffy. Gradually add confectioners' sugar, beating well after each addition and scraping sides and bottom of bowl frequently. Add milk; beat until light and fluffy. (If frosting is too thick to spread, gradually beat in additional milk.)
Divide frosting evenly into 4 bowls. For a Blue Unicorn Frosting, stir in 1/4 teaspoon of the Sky Blue color and 2 teaspoons Raspberry Extract into 1 bowl. For a Purple Unicorn Frosting, stir in remaining 1/2 teaspoon Sky Blue color, 1/4 teaspoon of the Berry color and 1/4 teaspoon Lemon Extract into second bowl. For a Pink Unicorn Frosting, stir in remaining 1/4 teaspoon Berry color and 1/4 teaspoon Lime Extract into third bowl. For a White Unicorn Frosting, leave fourth bowl untinted. Fit a pastry bag with a large star tip. Fill bag with the 4 colors of frosting, placing them side by side in bag. Pipe frosting onto cooled cupcakes. Decorate with sprinkles, if desired.
If a pastry bag is unavailable, place 1 tablespoon of each color frosting on each cupcake. Spread and swirl frosting with small knife or spatula.