Prepare lime, orange and 1 package of strawberry Jell-O as directed on the packages.
Pour each flavor into separate 8-inch square pans. Refrigerate 4 hours or until firm. Cut into 1/2 inch cubes; measure 1 1/2 cups of each flavor. (You can use the remaining cubes for garnish if desired, or for snacking).
Stir 1 cup boiling water into remaining package of lemon Jell-O in a medium bowl until dissolved completely. Stir in 1/2 cup cold water. Refrigerate 45 minutes or until slightly thickened (consistency of unbeaten egg whites). Stir in 1/2 of the Cool Whip
Gently stir in measured gelatin cubes. Pour into a 9 x 5-inch loaf pan. Refrigerate overnight. Unmold and garnish with remaining gelatin cubes and whipped topping, if desired.