I am probably a bit of a maverick in that I pre-wash some things and not others. Solids most often get pre-washed as do batik pieces if they are in a quilt rather than a wall hanging that will probably never be washed. I have never had a problem with mixing washed and unwashed fabrics. And, after all, most quilts will be washed. I wash mine before I give them away or use them to remove starch, glue or anything else that might be there. I so use color-catchers for all washing processes. I just try to be practical and use my time and energy wisely.