Preheat the oven to 180°C (160°C for fan assisted ovens)/Gas Mark 4. Line 2 x 12-hole muffin trays with paper cupcake cases (see tip).
Stir the cake mix, oil, water and eggs together gently in a bowl, then whisk (by hand or with an electric mixer) for 2-3 minutes, until smooth and creamy.
Divide the mixture equally between the paper cases and bake for 18-22 minutes until risen and springy to the touch. Remove from the oven and cool in the muffin trays for 10 minutes, then transfer to a wire rack and leave to cool completely; about 30 minutes.
Divide the icing equally into three bowls (approximately 200g in each bowl). Beat in enough green, yellow or blue food colouring gel or paste into each bowl to give a good strong colour.
Using a small palette knife, frost 8 of the cupcakes with the green icing, 8 with the yellow icing and 8 with the blue icing. Decorate with the sweets of your choice.
To serve, assemble the cupcakes (in their colour blocks) to spell out the word DAD.