I don't prewash and do use a lot of Kaffe fabric. AFter finishing a quilted project with Kaffe fabric in it, I use Shout color catchers to wash the quilt and was as many times as needed until the color catchers come out clear.
I just made a quilt that had a lot of Kaffe fabric with black background and intense colors including bright reds. Didn't prewash but washed 3 times with color catchers and final wash without color catcher after quilt was finished. No bleeding but the first 3 color catcher washes did capture colors from the quilt fabrics including black and red.