http://sewingoutofmycomfortzone.blogspot.com/2012/01/how-many-color-catchers-do-you-need.html
Here's my latest experience. I just bought 4 1/2 yards of red flannel for backing for two quilts. I always wash flannel before using it because flannel shrinks so much, and since it was red, I threw in 4 color catchers. This is what they looked like after the first wash with cold water.
I know there are only 3 in the picture. I don't know what happened to number 4. Down the drain, maybe, or wrapped up in the flannel.
In any event, I knew I had to wash the flannel again. This time I tried warm water. The color catchers still came out pink. I washed it a total of 8 times, twice in hot water, until I got color catchers that could pass as light pink.
That's acceptable to me. It is in the dryer now.