With an adult's help, chop the celery heart into small pieces. Using clean hands, pull apart the surrounding whitish leafy stalks, leaving them long and stringy; these celery pieces will be your seaweed. Set aside.
Drain the jar of artichoke hearts and cut into the size of a penny.
Prepare soup according to directions. Add the celery and artichokes and heat until soup comes to a boil. Turn heat to low and carefully add two or three drops each green and blue food coloring until the soup reaches an appropriately murky seawater color.
Carefully ladle the hot soup into individual bowls and sprinkle a quarter cup of crackers on top of each one. Encourage some of the floating celery seaweed to hang over edge of bowls and serve. Artichoke pieces and rice from the soup will sink.