I always pre-wash because that was stressed when I decided I wanted to learn how to quilt. My sister-in-law spent about a year making a quilt by copying family pictures onto fabric. Finally finished it early this year. Unfortunately, she had used some bright red fabric to set off all the pictures and as a border. She didn't pre-wash, and, yes, it turned the whole quilt a nice shade of pink. She washed it several times, but it seems the quilt is permanently pink.