I don't pre-wash everything. I do pre-wash colours that are intense reds, purples etc. If I am in doubt about a fabric, I cut a sliver off across the width and wet it in the sink of warm water. I then squeeze out most of the water and leave the wad of fabric on top of white paper towel to dry. If any colour comes out in the water or there is a stain on the paper towel, I pre-treat it before use. I keep both retyne (before using fabric) and synthrapol (already in quilt) in the house along with my Shout colour catchers for quilt care.