Now that I have a dual extruder Ultimaker, I revisited my first model uploaded on Thingiverse.
I have no idea how people print dual extrusion with other software. But use the _a and _b stl file as you normally would.
I'm working on the software for the Ultimaker, as you can see on the photo, there is a "minor" oozing issue to solve. The print also de-attached it self from the bed before it was finished, and the 2nd color didn't come out at the start.
I printed it to see if my heads where on the same level, which they are. So I'm very happy about this print.