Dissolve each flavor of jello completely in 2 cups of boing water in separate bowls. Stir 1 cup of cold water into each bowl. Pour into separate 9x13" pans. Refrigerate at least 3 hours until firm. Cut into 1/2" cubes. Place blue jello cubes in bottom of clear glass trifle bowl. Top with 1/3 of the Cool Whip. Add cake cubes, then sliced strawberries. Top with another 1/3 Cool Whip. Add the red jello cubes and then the remaining Cool Whip. Sprinkle blueberries over top if desired.