Shout Color Catcher and Carbona Color and Dirt Grabber claim to trap what the textile industry calls "fugitive dye," color that has bled from cloth. Boxes of Shout, a disposable sheet, say, "Allows mixed washes" and "prevents color runs." Boxes of Carbona, a reusable terry cloth, say, "Wash mixed colors with confidence!"
We found a brand of red polo shirt that bleeds reliably and washed identical shirts plus white cloths with and without Shout and Carbona. We judged the results with human eyes and with a colorimeter, which measures color change.
With or without the products, the white cloths turned pink. The Shout and Carbona sheets turned an even darker pink, meaning they did catch color. But they didn't catch all of it. Follow Mom's advice: Wash lights and darks separately, and wash anything that might bleed by itself or with a similar color.