I don't pre-wash fabric's. I always check to make sure the bolt board says pre-shrunk before purchasing any fabric.I figure if it's pre-shrunk it has also done any bleeding it's going to do. I wash every thing in cold water. About the only colors that worry me are those in the red family so I wash the finished quilt with an old white towel. So far the towel is still bright white. The only time I use dark solid colors in a quilt is if it is specifically requested.