I have only just found out about this the hard way! Doing a charity quilt the backing was a cheap bright red duvet cover and it crocked!
http://artisanssquare.com/sg/index.php?topic=12012.0
My new £1200 sewing machine now has a pink hue on the bed which won't come off. I must admit I haven't tried anything to harsh as I am worried about damaging the sheen of it, so beware of cheap fabrics, they crock!