Beautiful Quilt!
The one thing that comes to my mind, is that the quilting won't show on the dark fabric, if you use a dark thread. So if you didn't want to distract from the quilt design, you could just do all of the quilting in the dark fabric.
On the other hand... if you want to show off some spectacular quilting, you'd work something in the cream and lt. purple areas. That's where I draw a blank. I like to put a clear plastic sheet on top of my quilt, and doodle on it with a dry erase marker until I like what I see.