I have been commissioned to make a tee shirt quilt for the Pinhoti Trail Run in November. I'd like to make it 3D but not use black as the shadow. I'm using denim look fabric for the background and backing. It looks like denim patches and is mostly a medium blue color. Can I dye the fabric darker and use it for the shadow, or will it eventually fade? The quilt is going to be a gift to the only runner to participate in all 10 runs, so I hate to mess it up.