I was recently hired to create a cake/cupcake tower for a baby shower. The mom-to-be is having a boy so I picked the theme "What are little boys made of? Frogs and snails and puppies dogs tails".
The cake was a two layer chocolate cake with chocolate frosting. It was decorated with fondant, butter cream frosting, and royal icing.

The cupcakes were yellow cake with butter cream frosting and coordinating jimmies.

Butter Cream Frosting
Source: Cooks Illustrated (found on annies-eats.com)

2 ½ sticks unsalted butter, softened
2 ½ c. confectioners’ sugar, sifted
1/8 tsp. salt
2 tsp. vanilla extract
2 tbsp. heavy cream

In a stand mixer fitted with the whisk attachment, beat butter at medium-high speed until smooth, about 20 seconds. Add confectioners’ sugar and salt; beat at medium-low speed until most of the sugar is moistened, about 45 seconds. Scrape down the bowl and beat at medium speed until mixture is fully combined, about 15 seconds. Scrape bowl, add vanilla and heavy cream, and beat at medium speed until incorporated, about 10 seconds. Then increase the speed to medium-high and beat until light and fluffy, about 4 minutes, scraping down bowl once or twice. Add desired coloring and beat another minutes until color is evenly distributed throughout the frosting.