The T-shirt we all know today is an apparel

“[The T-shirt] is a really basic way of telling the world who and what you are.” — Dennis Nothdruft

When printing with water-based and discharge ink, the ink actually removes the color of the cotton in the fabric, replacing it with the color of the ink. The agent in the ink (known as discharge) only removes the color in the cotton though, meaning that with tri-blends, you'll be able to see some natural heathering in the shirt.