In a bowl, dissolve the lime gelatin in 3 cups boiling water. Pour into an 8-in. square dish coated with cooking spray. In another bowl, dissolve orange gelatin in remaining boiling water. Pour into another 8-in. square dish coated with cooking spray. Refrigerate for 4 hours or until very firm.
In a small saucepan, sprinkle unflavored gelatin over cold water; let stand for 1 minute. Add grape juice. Heat over low heat, stirring until gelatin is completely dissolved. Pour into a large bowl; refrigerate for 45 minutes or until slightly thickened. Fold in whipped topping.
Cut green gelatin into 1/2-in. cubes and orange gelatin into 1-in. cubes. Set aside 8-10 cubes of each color for garnish. Place 2 cups whipped topping mixture in a bowl; fold in remaining green cubes. Spread into a 13x9-in. dish coated with cooking spray. Fold remaining orange cubes into remaining whipped topping mixture; spread over bottom layer. Sprinkle with reserved green and orange gelatin cubes. Refrigerate for 2 hours or until set. Cut into squares.