Good point. There should be scraps around somewhere. One difference is that the markers were on the quilt for longer than it is on test pieces (I did test all the markers before), including a certain level of warmth from the room temperature, so I don't know if that will have set the markers a bit.
I'm sure I had colour catchers around once, but I have no idea where they got to. Oh well, they're easy enough to get hold of. Does anyone know whether they can react oddly with the marker pens? I'm thinking mainly of the Crayola washable markers, since the turquoise quilting marker should wash out when I soak the quilt before putting it in the machine.