While commercial color catcher products are available, you may prefer to make your own after reading the post on
One Good Thing.
Color catchers are useful in everyday loads of laundry with "mystery" fabrics that look like the colors may bleed or when washing items like quilts with a mixture of many dark colors like purple, red, blue, combined with white.
They also work when laundering knit or crocheted items - by hand or in a machine.
** I've only used manufactured color catchers, so I don't know if the DIY ones work as well.