Here's my how-to:
1 bag uncooked white rice
Desired colors food coloring
Separate rice between baggies, pour in 2 tablespoons of vinegar/1 cup rice.
Add 4 drops of coloring/1 cup rice.
Squeeze out air and seal baggy.
Pour rice out onto a flat baking pan and store in a safe place (turned off oven) until dry.