I used a basic white cake recipe which I divided into six and mixed in about 20 drops of food colouring in each (mixing half and half for orange and purple). A teaspoon of each coloured batter went into the cupcake liners before baking. A gentle drop was enough; moving the batter around isn’t recommended since it’ll encourage mixing of the colours. It yielded 16 cupcakes, instead of the 24 since the layers piled up pretty fast.
I also made a plain white cream cheese frosting, half of which I coloured black.
Decorations included sugar crystals, nonpareils, chocolate and rainbow sprinkles, and chocolate chips.
I might post close ups of some of these beauties. They were almost too pretty to eat!