I have made many rag quilts....never had a problem. They tell you NOT to prewash the fabric...I always do. I dont want to make something and then have the dye run all over everything. Even then, when I wash it, I still use a color catcher sheet with it. Make sure to use at least at 1/2 seam AND SHORTEN YOUR STITCH length. Good luck...I LOVE rag quilts.
Margie