I soak fabrics in separate containers and look at the WATER to see if it has colored.
I keep changing the water until it runs clear (or clear enough) - and if the fabric does not stop releasing dye/color, I discard it.
I had a problem with a washed fabric bleeding when I sprayed it with starch or sizing (don't remember which one it was) - if I remember correctly, they were a dark blue and a dark red RJR fabric