feed sack fabric was often combined with dressmaking fabric for these types of quilts. There also appeared to be a variety of muslin type fabrics. You might post your question on the site for The Feedsack Club for indentification of the background fabric. I have some of these old tops and often there was differences in quality and type of background fabric. White feedsacks were sometime used as well. There are many interesting stories of folks being taken when their father bought grain and feed to choose the printed sacks for their next dress or other garments.