Prepare 1 small box each of orange, cherry and lime gelatin, dissolving each one separately in 1 cup boiling water and then adding 1/2 cup cold water. Pour each flavor into a separate 8-inch square pan. Chill at least 3 hours. Cut into 1/2-inch cubes. Set aside a few cubes for garnishing.
Dissolve 1 small box lemon gelatin with 1/4 cup sugar in 1 cup boiling water. Add 1/2 cup pineapple juice. Chill until slightly thickened. Blend in 4 cups whipped topping (Cool Whip