I originally printed directly on the blue t-shirt, messed up and washed the ink out as best I could. A shadow remained, so rather than reprint over the shadow, I found an old too-small taupe t-shirt and printed the design in blue on that, cut it out, and sewed it (ie. appliqued) onto the blue t-shirt, covering the shadow.
I was immediately fond of the result. And I suddenly have a use for the old t-shirts that I don't wear but have been too lazy to donate!