Preheat the oven to 350 degrees F. Coat a 9-inch square (2 1/4-inch-deep) cake pan with cooking spray. Prepare 1 cake mix as directed, beating in 1/2 teaspoon almond extract. Tint pink with gel food coloring. Transfer to the pan; bake about 35 minutes. Let cool.
Repeat to make a yellow and a green cake. (Bake both cakes at the same time if you have 2 pans.)
Trim the tops of each cake with a long serrated knife to make level.
Put the pink cake, trimmed-side up, on an inverted baking sheet. Spread with 1/2 cup jam.
Top with the yellow cake, trimmed-side up; spread with the remaining 1/2 cup jam, then top with the green cake, trimmed-side down. Freeze the stack 1 hour.
Microwave the chocolate and butter together in a microwave-safe bowl in 30-second intervals, stirring, until melted and smooth. Let cool slightly.
Using an offset spatula, spread the chocolate mixture in a thick layer on top of the cake.
Use the tines of a fork to create wavy lines in the chocolate. Return to the freezer until the chocolate is set but not hard, about 15 minutes.
Trim all four sides of the cake with a long serrated knife. Transfer to a platter.