Rinse out the shirt in warm water, then ring it out until it's damp. Decide where you want the center of your design to be. All the rings of the pattern will radiate out from one central point, so choose this spot and pinch up your shirt right there. Wrap a rubber band around the shirt very tightly at this point.
Grab the shirt from the rubber-banded spot and pull it into a rope shape. Wrap rubber bands around the shirt rope every couple of inches until you have bands along the entire length of the shirt.
Mix your dye baths according to the package directions. Most dye bath products call for mixing in 1 cup of salt with the dye solution, to keep the dye permanent in the fabric. Measure the salt and dye powder carefully to create the correct solution for dyeing.
Dip one end of the shirt into one color of dye and the other end in another color. Leave the shirt ends in the dyes for at least five minutes. The longer you leave them, the brighter the color will be. If you want a third color in the middle, hang that portion of the shirt into a third color bath. Use rubber gloves while dyeing the entire shirt, unless you want hands that match your wardrobe.
Place each T-shirt in an individual plastic bag and allow it to sit overnight. This will make the colors pop, causing them to be brighter and more eye-catching. Rinse the shirts the next morning. Start with warm water and gradually go to cool. Rinse with the rubber bands on first, then take them off while still rinsing. Don't stop until the water runs completely clear.
Wash the shirts in cold water in the washing machine, then hang on a line to dry, out of the sunlight.