Make layered cake. Prepare batter following recipe directions. Divide batter into five equal portions. Tint each portion a different shade of violet, from deep to light. Bake and cool cake layers in pan set according to pan package instructions.
Fill cake. Prepare buttercream icing. Tint portions dark, medium and light violet. Reserve some white. Place first layer on cake circle. Use spatula and white icing to ice top layer smooth and stack with next layer. Continue icing and adding layers.
Decorate cake. Place cake on cake turntable. Use spatula and dark violet icing to ice bottom third of cake smooth. Use spatula and medium violet icing to ice middle third of cake smooth. Lightly blend tone transition between dark and medium violet icing. Use spatula and light violet icing to ice top portion of cake smooth. Lightly blend icing tone transition between medium and light violet icings. Use spatula to make icing lines on cake.