Small plastic bowls
Note: Use different flavors/colors of Kool-Aid.
For every color you wish to use, put 1 package Kool-Aid and 1 ounce of vinegar in individual plastic bowls. Mix until Kool-Aid is dissolved. Using rubber bands, pull and twist T-shirt into different shapes. Dip rubber-banded ends in bowls (make sure you wear gloves or your hands will stain). To set colors, iron on medium-high using an ironing cloth between shirt and iron. Let set for 24 hours before washing. To be safe. wash separately the first time. Launder T-shirt as usual and it's ready to wear.
Note: Don't put softener on the T-shirt if you pre-wash it as the dye will not take.