You can test by dropping a small piece (maybe 2" square) in a glass of water for a few hours; watch to see if any dye bleeds into the water. While the fabric is still wet, rub it against the other fabrics used in the quilt to see if any dye transfers that way. If the fabric passes both tests, it is okay to use.
However, the dye-setting properties of Retayne are supposed to be lost if the fabric is washed in hot water later. To be absolutely certain the quilt will be okay, you could wash a small piece of the fabric in very hot, soapy water and then rub it against the other fabrics in the quilt. If no dye transfers, it will be fine even if the quilt is washed in hot water later.
One thing to keep in mind is that dye in the water is not the absolute determining factor that would keep you from using it in the quilt. Not all fabrics pick up stray dye. If the other fabrics in the quilt do not pick up a bleeding color, it doesn't matter if the fabric continues to bleed (except that the fabric will fade more with each washing).