A little show and tell.......and well, eat :)
For the icing, I used pre-made butter cream icing. I just separated that as well and colored it with the same colors as before. But I also kept a little white left over for mixing the colors later. After you have the icing the color you want it, add some powdered sugar to stiffen it back up.
Once the icing is the way you want it, get a piping bag ready with a plain round tip. Add the icing one scoop at a time making sure to separate like colors so you get a good color mixture as its coming out of the bag. I did blue, pink, yellow around the lining of the bag and then white in the middle to start and then I just made sure to avoid putting like colors on top of each other. When you are ready to pipe, just start towards the rim of the cupcake and squeeze the bag with even pressure swirling towards the middle. For the little point, I just dipped/gently squeezed/raised the bag and let off pressure.