Here are some pointers: You want to act quickly because your macaron batter is with raw egg, so you don't want to take all day to do your own custom shapes. For dividing the batter into colors - you first have to make sure that your dry ingredients are fully incorporated, but JUST BARELY. Then divide and mix colors because you can't over beat the mix and flatten your meringue. That would be bad! :) Then pipe away - do what shapes your heart wants to see or eat! Don't be scared. As long as you've made the meringue correctly - you should see feet on your macarons and the shell should succumb to osmosis once filled - creating the ever-sought-out French Macaron. :) Of course, this is my first time doing shapes, so I'm no pro at it. But with satisfactory result - I'd say that I'm willing to try again when inspiration hits.
Inside look on the process: it's similar to wet-on-wet with sugar cookie decorating. But it's relatively new - so I don't think this art even has a name yet.