However....if all of the fabrics in the quilt are deeper, richer colors, you may not notice as much if you get a little bleeding. Mixing those deep greens and purples with any white or very light fabric is where you could have really run into trouble.
On the quilt I'm working on now, I considered doing some accent pieces in white...but almost all of the rest of the quilt is various colors of hand-dyed fabric and batiks. No way will I flirt with disaster by adding whites into the mix.

I always Pre-wash.

Some fabric fades or bleeds &
some Shrink.

Tooo much work to have a puckery off-colored quilt.

It interesting to me that it seems that the issue of bleeding fabric has gotten worse not better over the years . There was a time I did not prewash and had no issues. Now I pre- wash because its seems there are more fabrics that are bleeders than there was years ago. Way back when I first started sewing .. red was always a highly suspect color... so we prewashed any red fabric.

I agree Lori S. There was a time when fabrics didn't bleed like now.
It's not that I mind washing the fabric OR that it's trouble. Knowing I'll have to iron that fabric to make it ready for quilting is what has been holding me back. OH WELL... guess I'll get friendlier with the iron! ;)

This is why I always prewash, I just like all the chemicals out before I use it!!!

When I prewashed I did 4 small loads - one for each color. Then I had to cut the frays that had the fabric twisted up. (I had unfolded each piece before I put it in and each piece came out twisted from the fraying threads.) After the dryer I had to cut the pieces apart again - because of the threads. Then I starched and ironed each piece. So more trouble? Yes!

The quilt will have large sections of tone on tone cream fabric. The part that bled was the backing - I'll probably wash it again before I put it together.

Here's what I'm making: (It will be 90 X 90)

Washing and drying is not the biggest issue for me....it is all of the straightening, starching and ironing that I object to. I pre washed a few yards waaaay back when and then never again. It takes way too much of my time away from the creating, piecing and quilting. I buy yards and yards of fabric and am not willing to spend time pre-washing.....just sayin.....:) I have yet to have a regret or ruined quilt. To each his own though.

I'm a prewasher mainly because the fabrics that I used to make my clothes shrink so this ensures my new dress still fits after the first washing.
BUT.... aside from the color catchers... I use a 1/2 cup vinegar in new fabric or brights... that sets the color and reduces the fading

To stop the twisty tangle... Serge (zigzag) the cut ends.... stops the fraying that tie up your yards of fabric into masive balls of mess....

Yikes! Never through away fabric, especially batiks, lol! I make a lot of wall hangings that would rarely if not ever be washed. Anyone wanting to throw bleeding fabric away can always mail it to me....I'd be glad to pay the postage. Just can't imagine throwing fabric away. :)

When I took classes, my teacher was strict about prewashing. First soak it in salt water, then prewash and dry it in a hot dryer. A few times I had colors bleed terribly. For me mostly greens. I hate to think o all the hard work ruined if I didn't prewash.