Bake cakes. Prepare cake mix following recipe instructions. Bake and cool two cake layers. Trim layers to 2 ½ in. each. Fill and stack layers for 5 in. high cake.
Ice cake with white icing, using icing smoother to smooth cake on top and sides (cake should not show through icing).
Make heart template. Print and cut out heart template. Using pencil, trace heart on parchment paper. Cut out heart.
Place heart on side of iced cake. Using pencil or tape, mark arrow on cake board where heart is placed (this makes it easier to find later).
Make cake strip template. Measure circumference and height of cake. Cut a piece of parchment paper to fit the circumference of the cake, adding one inch on both sides to allow room to handle the parchment strip.
Cut the strip to the height of the cake.
EX: For a cake 5 in. high and 22 in. around, the final strip should measure 5 in. high and 24 in. wide.
Tint icing. Tint ¼ cup icing each dark pink and light blue using color combinations provided. Combine Aster Mauve and Pink icing colors to get light and dark pink colors shown. Combine Sky Blue, Teal and Kelly Green icing colors to get light blue color shown.
Using Teal icing color, tint ¼ cup icing dark teal and ¼ cup icing medium teal.
Using Lemon Yellow icing color, tint ¼ cup icing yellow.
Tint 2 cups icing light pink using color combination provided.
Reserve remaining icing white.
Make buttercream transfer. Tape parchment paper strip template to surface.
Prepare five decorating bags with tip 2. Fill separately with dark pink, light blue, dark teal, medium teal and yellow icing.
Alternating colors, pipe random shapes on parchment paper template, excluding the extra inch on both ends of strip.
Freeze template until buttercream is set, about 20 minutes.
Once set, remove template from freezer. Working quickly, use spatula to ice light pink icing evenly over strip, about ¼ in. to ½ in. thick. Be careful not to push the icing down too hard, as that could smear the shapes on the template.
Return template to freezer, letting it chill for 5 to 8 minutes. The icing should be set, but not completely frozen.
Add transfer to cake. Carefully wrap buttercream transfer around sides of cake, using a fondant smoother to press the strip to the cake evenly.
Return cake to freezer, leaving parchment paper on cake. Chill for about 10 to 15 minutes. Slowly peel away parchment.
Using a tapered spatula, remove any excess icing on top of cake.
Decorate cake. Using the heart template as a guide for the size and placement of the heart under the pink buttercream, use an angled spatula to remove small amounts of pink buttercream until heart is revealed. Using edge of spatula, remove parchment paper heart from cake.
Prepare decorating bag with tip 2 and remaining white icing. Pipe message on cake. Transfer to serving plate or board.