I'm a prewasher of everything. I recently washed a finished quilt before I gave it to my son. Knowing I had prewashed, I hesitated before I used a color catcher. Its a big quilt, so just at the last second I added 2 MORE color catchers. They came out dark navy blue! I wish I had added more as one of the white fabrics and two off white picked up dye. I'm glad I prewashed it as he would not have put in that many color catchers. AND if I ever get out a dark one when I prewash, I will keep washing till the fabric quits bleeding..OR throw the fabric out!