Referring to Pillow Back Assembly Diagram, join the remaining four assorted print 5-inch squares in pairs. Press seams in opposite directions. Join pairs to make the pillow back. Press seams in one direction. The pillow back should be 9-1/2 inches square including seam allowances.
Layer the pillow back, a batting square, and a muslin inch square; baste. Quilt as desired. In the same manner, layer and quilt the remaining two muslin squares and batting square to make a quilted pillow top.
With right sides together, sew the quilted pillow top to the quilted pillow back to make the pillow cover, leaving a 3-inch opening along one edge for turning. Turn the pillow cover right side out. Stuff with fiberfill through opening. Whipstitch the opening closed.
Lay out yo-yos in six rows. When pleased with the arrangement, whipstitch yo-yos together, stitching about 1/2 inch along edges with right sides together. Join rows in same manner to make a yo-yo square.
Center and pin the square to the quilted pillow top. Whipstitch the outer edges of the yo-yo square to the pillow top seam lines to complete the pillow.