Hi
I have a blue bobbin case for FMQ and I use it all the time. It is an extra bobbin case, that has a blue dot at the place where the threat leaves the case and is put out and then up towards the needle. The normal Janome bobbin case has a red dot at that place.
It is a normal bobbin case just with a looser adjusted thread tension. Since a slightly lower tension is required for FMQ one could also just loosen the thread tension at the red case. It is however more convenient to change the bobbin case, instead of everytime readjusting the tension when changing from piecing to quilting and back.