Make this chocolate cake for a party and let kids decorate different parts of the cake to create an edible collage.
Preheat oven to 350°F. Spray a 9 x 13-inch cake pan with canola oil; set aside. In a large mixing bowl, combine mix, cocoa powder, buttermilk, oil and eggs. Blend for 1 minute, scraping the sides of the bowl. Beat an additional 2 minutes; stir in chocolate chips.
Pour batter into prepared pan. Bake for 35 to 40 minutes, until firm to the touch and cake pulls away from the sides of the pan. Allow to cool in the pan for 30 minutes before unmolding. Frost when thoroughly cool.
Add several drops of blue food coloring to vanilla frosting. Mix well and spread over the entire cake, smoothing as evenly as possible. Set aside.
Place remaining decorating supplies on the table. Allow each child to decorate a section of the cake.