I don't normally go for things like this but in an effort not to ruin the fabrics I spend money on I thought I'd give it a try. They really work! All you have to do is put a sheet in with your wash and it will catch all of the excess color that runs out of your fabrics. I have been using it when I'm washing quilting fabrics that have red in them. I assume it works the same way for washing things like dark denim with lighter colors.
I got mine at Target. The difference is actually more obvious in person than in the photos.