2 T. white vinegar
10 drops food coloring
quart mason jar with lid
Measure the rice into the jar. (If you are feeling particularly patient, your toddler would love to help with this.) Add vinegar and food coloring. Screw lid onto jar and shake until rice is evenly colored. Line cookie sheet with foil. Pour rice onto foil and bake in a 200 degree oven for about 30 minutes, or until rice is dry. Allow to cool. Store in a closed container.
I just came across a blog post on It's A Preschool Party which shows how rice can be dyed using unsweetened drink mixes. Not only is the rice colored, but it is scented too! Check out her Smell Good Supplies.