Since many quilters use precuts, it is not recommended that the precuts be washed because it distorts them and they fray. If you are using only yardage it's your call. But I think most people think do one or the other, but don't mix. I've mixed and haven't had any disasters. Many people use the Shout color catcher cloths in their washers during the first washing of quilts that had fabrics that had not been washed. The red next to the white is a problem, but the color catcher (some people use more than one) should take care of it. The only advice I've heard forum members say is to definitely prewash flannel, because it shrinks so much, it would distort the quilt badly if used unwashed. I myself have never had a problem with color bleeding, and if I am unsure, I use the color catchers. You find them in the laundry section by the dryer sheets. I get mine at Target.