A couple of years ago Barbara Brackman gave me a stack of appliqued bird blocks that she had started but did not want to finish. The background fabrics were too dark and the birds were blending in too much. I have done this same thing myself...I once appliqued a completely invisible toy train with 30s reproduction fabrics. Anyway, the blocks sat around until I found products called Decolorant and Decolorant Plus. You brush this jelly-like stuff on your fabric, let it dry and then steam iron it. Decolorant lightens the fabric, but Decolorant Plus lightens the fabric and replaces it with a new color. Here are some of the original blocks:
Here are two that have been "decolorized":
The bottom one had plain Decolorant used on it. The top one had a mixture of plain Decolorant and White Decolorant Plus used. I masked off a dot design using pricing stickers from Office Depot before brushing on the Decolorant, and tried to avoid the birds. (You can see that I did not get close enough to the bottom of the bottom bird.) So the dots are the original fabric colors. Then I finished and highlighted the birds with free-motion machine stitching in black thread and sewed the blocks together. Barbara had planned to do an Irish Chain sashing, so some of the blocks had green squares appliqued in the corners. I skipped that part and did not even finish up the missing corner squares. I thought quilting those squares in would be a nice effect, but it doesn't show as well as I had hoped. I'm pretty pleased with the result, although anything with a bird on it looks good to me.