1. make whatever cupcake mix you like to use
2. divide the mixture into 6 bowls:

bowl 1 - add half a cap of red food colouring
bowl 2 - add half a cap of red & half a cap of yellow(for orange)
bowl 3 - add half a cap of yellow
bowl 4 - add half a cap of green
bowl 5 - add half a cap of blue
bowl 6 - add half a cap of blue & half a cap of red(to make purple)

3. layer the colours in your cupcake tray(in paper/cone cups) as follows:
purle
blue
green
yellow
orange
red

4. put them in the oven and then ice or decorate however you want :)