I believe they should be left as is. They are original and have memories attached. The difference in muslin color only adds to the 'mystique ' of these blocks. When you shop for background muslin, choose different shades of muslin to compliment the ones you already have. 'Treasureit' also has a good suggestion about using some complimentary solids for backgrounds. Please keep us posted.... p.s. 'Iclang' also has a good suggection