It is hard to find a good quality muslin for piecing into quilts nowadays. I usually go with a white on white fabric if I am piecing. HOWEVER since is looks as if the muslin is intended for foundation piecing on than the thinness would be an asset. Any lightweight light coloured fabric that won't show through the fabric sewn onto it will work. The reason you use a lightweight product for foundation piecing is so the layers of the quilt are not too hard to quilt through later.