I've used standard discharge techniques in several ways with excellent results in art quilts and have been wanting to try the discharge pastes and gels since I first read about them.
That said, there's an excellent article by Ana Buzzalino in the Aug/Sept 2010 issue of Quilting Arts about discharge paste (they used Jacquard) and how you can add fabric paint to it. When you do that, the original color of the fabric is removed and it is replaced by the color of the paint.
Discharge paste is also discussed in the book The Painted Quilt, by Linda and Laura Klemshall.