Heat oven to 350°F. Grease two 9-inch round cake pans. Prepare cake mix according to package directions. Bake 30 to 35 minutes, or until a toothpick inserted in center comes out clean. Transfer to wire rack; cool 15 minutes. Invert cakes onto rack; cool completely.
Spoon 1 cup frosting into pastry bag fitted with 1/2-inch star tip. In medium bowl, tint remaining frosting with violet paste to desired color. Level top of cakes. Place 1 cake layer on serving plate; spread with 1/2 cup violet frosting. Top with remaining cake layer. Spread sides and top of cake with violet frosting.
Dip lollipop tops in water, shake off excess, and roll in colored sugars. Place on plastic wrap, sugared side up, to dry. Repeat process with purple Neccos and sugar.
Randomly pipe stars of white frosting onto sides and top of cake. Gently push Necco Wafers, sugar side out, into white stars. Place lollipops and candles in center of cake.