Preheat oven to 180C/350F/Gas 4 and place 24 white cupcake liners into cupcake pans. Set aside.

Make cake mix according to box instructions and divide it into 3 bowls.

Add orange food coloring to one of the bowls and stir to combine to desired shade.

Add yellow food coloring to another one of the bowls and stir to combine to the desired shade.

Leave the third bowl uncolored (white).

Divide the orange cupcake batter between the 24 cupcake liners, enough to cover the bottom.

Repeat with the yellow cupcake batter on top of the orange batter.

Finally, add the white batter on top.

Bake for the instructed time on the box (around 20 minutes). A toothpick inserted into the center of the cupcakes should come out clean when they are done.

Remove from the oven and allow the cupcakes to cool in the pan for 5 minutes before transferring to a wire rack to cool completely before frosting.

To make the frosting, use an electric stand or handheld mixer and add the butter, powdered sugar, vanilla, and cream to the bowl.

Beat on medium speed until creamy and smooth and stiff peaks form.

Scoop 2 cups of frosting into a large piping bag fitted with a large star tip. Set aside.

Divide the remaining frosting into three bowls.

Add purple gel food coloring to one, orange to another, and green to the third. Stir to combine to desired shade.

Fit a piping bag with a small star tip (Wilton #22).

Add the purple frosting down one-third side of the piping bag.

Add the orange frosting down another one-third side of the piping bag.

Add the green frosting down the remaining one-third side of the piping bag.

To decorate the cooled cupcakes, use the bag of white frosting to pipe swirls on top of each cupcake.

Place the horn in the middle of the frosting, with the ears to either side of the horn. Place the eye sprinkles below the horn.

Use the tri-color frosting to pipe the unicorn's mane around the horn and ears and down the sides of the cupcake.