I don't think there is a concrete answer to washing or not washing, I don't always prewash, unless it's red, green, black or I'm suspicious. I sometimes cut off a small piece, soak it in hot water for a few minutes, then lay it between 2 pieces of white paper towel to see if it has faded. I have been told that when you wash a whole quilt that the soap, not detergent, makes a big difference. A nationally known quilter told me that Dawn dishwashing soap is a good one to use, as well as Ivory and of course, Orvus. Orvus is the one I use 99% of the time. I also use it for better clothing that is washable. I bought a gallon of Orvus at a Vet/animal shop years ago and I'm still using it. So whether you wash or don't wash before you make your quilt, choose your soap carefully when the time comes to wash it when it done.