The "color" is excess dye coming off the fabric - the other fabrics that absorb it are then permanently dyed and it's almost impossible to remove.

I am very impressed with Color Catchers, but I only use them to wash new quilting fabrics. I don't use them in regular laundry. They are quite expensive, so I sort my laundry the old fashioned way to avoid color transfer.

I started using one a couple weeks ago when I got a batch of thrift store fabrics and wanted to wash them all at once. Worked great and now I use it with new clothes as well to make sure that new red tie-dye shirt doesn't bleed all over the other darks.