I wash mine with my regular detergent. However, I found that not only can fabric bleed, but it can crock too. I didn't worry too much about crocking until it happened to me. That when one fabric sticks on another fabric and sits there sort of stuck together. You can get color transfer just in that one spot where they sort of stick together. Color catchers only catch color from the water in the tub. I don't know if prewashing keeps that from happening because it's such a rare occurance. I don't want to prewash the daylights out of fabric, but I do prewash reds and stitck it wet between some white fabric and leave it there with something heavy on top to see what kind of color transfer might happen.