I thought it was pretty cool... I am sure this is some sort of style of painting (and if it has a name please tell me), but I am going to call it the creamsicle effect or maybe the rainbow sherbet effect. Regardless, I like it.
Now you may be asking yourself, "How on earth did she do something so complicated?" It's crazy, but I put the icer tip in a big piping bag and threw blobs of different colored buttercreams inside. I then piped it on the cake and smoothed with a bench scraper. Whew! Crazy instructions! Just remember the more you go over it with the bench scraper, the more your colors will meld. Doing it too much may lead you to a not-so- pleasant color.
If that is too much color for you, try just two colors. Off the top of my head blue and white would make a nice combination to give a lightly clouded sky or underwater effect... or for just a whimsical kind of look... pink and white. With this cake, I added pink at the bottom or the bag and white at the top. This gives more defined color areas.
So the next time you need to make a quick cake for a party, use up all those little leftovers and see what you get. If you really don't like it, you can always cover it in fondant!