I use Woolite and fabric softener. The last one I just finished was red-white-and-blue and some of the fabric had not been prewashed. Tossed 3 color catchers in a mesh bag (because we have a front loader) and washed in cold. Did that about 3 times until the catchers came out clean. Hindsight - I should have gone to the Laundromat.
Color catchers come about 25 to a packet and they are relatively inexpensive.