I know I've posted this before, but needed to again. I stopped prewashing my fabrics a few years ago. And have never had any problems. Of course, I do use a color catcher when I wash the finished quilt. Now, if I have a very bright color, I will prewash that piece. I also mix up the washed & unwashed pieces I've swapped. Again, never had any problems. Maybe, I've just been lucky.