IF... a teenaged son spilled spaghetti sauce on the newly-made quilt, and panicked, and dumped it in the machine with hot water and detergent, set it on the long cycle... or let it soak for two days... would the fabrics bleed? [This is a worst-case scenario in my mind.]
My philosophy on pre-washing is to MAKE SURE the fabrics will not bleed in an insane situation such as that.
Often, fabrics will not bleed until they have been in HOT detergent water for 20 minutes (based on my washing experience).
I always separate by color families. I inherited a large (mostly unwashed) stash, and I put the darkest colors in the machine tub first. If all went well, I then added the brights, and then the lighter colors, after a time.
If the darks bled heavily, I washed them until they bled only a tiny bit before adding the brights. Colored water can/will color the lighter fabrics.
Color Catchers will not always pick up all the loose dye, if it is strong. I don't like to waste a Color Catcher until the bleeding is much lighter.
Let the fabrics soak in HOT water for 20 minutes... either in the tub washer, or on top of the stove in a big pot... if you only have a few fabrics in the same color family.
To keep the fabric from roping and shredding in the TUB washing machine, DO NOT AGITATE.
DO NOT let it agitate through the cycle. To prevent that, just keep the machine lid open. Swish the fabric around, periodically, with a large spoon or paddle.
I like using a Color Catcher, too, but it's not required. You can tell when fabrics are through bleeding. Teals, red-purples, reds, and even some browns have been heavy bleeders, in my experience. But I wash everything before putting it into my stash.
There are other points of view. This is mine.
Have fun with your bargello!
From Kathryn Kistner in Texas, who's now saying,
"DO NOT AGITATE, DO NOT AGITATE, DO NOT AGITATE..."