I also don't prewash my fabrics but I'll throw in a couple of color catchers on the 1st wash to a finished quilt. I'd rather it bleed on me than after its been given out as a gift then the receiver goes to wash it and it bleeds on them. One quilt bleed on me and I didn't catch it before I threw it into the dryer. Thought for sure it was ruined but someone here told me to go ahead and wash it again with another color catcher and it should come out. It did and I am so grateful for the person that told me to wash it again. Thank you whomever that was.
I have used solid black fabrics in a number of my quilts and have found them not to bleed as I would think they would. I have found Kona solids to bleed more than Moda solids so I tend to stick with Moda's fabrics.