Mimi Sharon wrote in the flannel for backing thread:
I use the salt and cold water, too! Even red holds it's color so well. My husband won't wear new jeans until I was them at least twice in salt water. He doesn't know it's salt water, he thinks I'm magic in keeping new denim from fading on him...
Read that thread and see what you think. I haven't tried it myself, but I always prewash. In case bleeding is an issue or shrinkage, I catch it before my innocent victim I gave it to finds the problem.
Let us know what happens. :-)