after mixing the cake up like normal, divide the batter evenly between 6 bowls. use food coloring to make your tie-dye colors. i went with: red, orange, yellow, green, blue, purple & kept them on the softer side for a springy rainbow.
put a (relatively) small spoonful of each color into each cupcake liner, stacking the colors on top of one another, not swirling.
bake as directed.
for the frosting:
divide between 6 bowls & use the food coloring to make the same colors as the cupcake batter.
fit a piping bag with a wilton 2d tip. put a spoonful of each icing in the bag. i went around the side with 4 colors & put the last 2 in the center. pipe to your hearts content!