You can use the shirt showing through as dots to alter the printed color, however… just remember one thing: Screen printing has this horrible characteristic called 'Dot Gain". If you have small dots of shirt showing through the ink (or what we call in the industry ‘reversed out’), they will tend to close in. This is true with reversed out thin lines too. Just be careful how much detail you are trying to print. As always, my OPINION is that a t-shirt should be viewed in about 0.4 seconds. Anything that takes any longer to see is a waste. If you are zooming in to look at individual pixels, you are printing on the wrong medium.