It's a bit of an illusion, but the quilt is all made with HST's. There are no inset/y-seams. You can see how each block is constructed.
My monitor is acting up so I can't quite make out if the other side of some of the larger HST (the plain side) is made up of multiple fabrics or not.
But the quilt is a lot easier to piece than you would think at first glance.