Chalk is OK. It tends to come off if I mark very far ahead of things, though. That could just be me.
Slivers of soap work well on dark fabrics. Remember to keep your fingers away from your face while quilting things marked this way. I've soaped my eye pretty good.
I've also used Crayola washable markers and wash away quilting pens on old quilts, too. There was no problem with either of these.
Try a few marks in a inconspicuous place and see what you can live with.