dunster - I don't follow what you mean by the top fabrics shadow on the quilt back. I did use a low loft W&N batting, but what I saw was definitely ON the fabric and not a shadow, although it gave the appearance of a shadow on the fabric.
I'm still going to try the Dawn and color catchers. When I checked on the quilt this morning I didn't see the shadowy spots on the green fabric anymore. Maybe the vinegar and cold water worked. Anyway, I'll be checking again tonight.