I generally prewash everything except the precuts. When the quilt is finished, I wash it with a few color catchers and have never had a problem. The precuts I have used were always the brand names, not the generic ones from Walmart or Joann's, so I don't know how those behave. I have never had any bleeding onto my quilts, but sometimes the color catchers come out dark. It's funny, I would expect that it would be the reds/blues/purples that throw off the most dye, but often it's the yellows/greens. I don't know why, just my experience.