I'm not a prewash person, definately not on precuts. I believe the makers recommend NOT prewashing. now i've never run into a problem either, with bleeding or shrinkage.

On the color catchers-they do work. A few years ago several of my kids were in food service, wearing white shirts with blacks pants. they would throw all their work clothes together in the wash to save time(they knew better but waited till the last minute to do their work clothes) the color catchers saved their white shirts from turning grey.