This suggestion would require a lot of twisting and turning of the quilt if you want to use a walking foot. But I was thinking of a square spiral in the striped squares. Start at one corner and quilt around all 4 sides. Stop about 1/2-1" short on the 4th side, turn and repeat around all 4 sides (stopping 1-2-1" short and repeat again). All of the white pieces are triangles. So you could repeat this quilting in the white triangles and this would result in triangular spirals. Of course, this would be a lot easier with a darning foot because you wouldn't have to twist and turn the quilt. The quilting lines wouldn't have to be exactly straight or symmetrical. It might even be more interesting if they were a little wonky.