The best way I would think would be to use a spray paint product. If its cloth, perhaps staining it may work. I would think it would depend upon what it is you want to end up with as well as what your going to start with as well.
Thanks for the answers, but I'm still hoping for more ideas.
You could use a highlighter, as Tuula did here:
What material is the lampshade?
Another option is to stencil a design and glue on some cute fabric trim.