I don't use pre-cuts much. But if I do, and they are darker colors, I will just soak them in warm water in the sink for 1/2 hour or so and see if any dye bleeds out. If not, I gently hang them to dry, iron and go on. If they bleed, I will refresh the water a couple of times until it stops. I don't put pre-cuts in the washer for fear to too much fraying. Just soaking them avoids that.