In a medium mixing bowl stir together graham cracker crumbs and butter. Line an 8x8x2-inch baking pan with heavy foil. Press crumb mixture into bottom of foil-lined pan; set aside.
In a large mixing bowl thoroughly combine flavored and plain gelatin; add boiling water. Stir until gelatin dissolves. Stir in the grape juice. In another large mixing bowl with an electric mixer on medium speed beat softened cream cheese until very smooth; very gradually beat in gelatin mixture, scraping sides of bowl as neded. Chill until partially set (the consistency of soft pudding), stirring occasionally. Fold in thawed whipped dessert topping.
Evenly space the 1 1/2 cups melon balls on the graham cracker crust, if using. Carefully pour the gelatin mixture atop the balls. Chill until top is set. Cover and chill 8 to 24 hours.
Using foil, lift dessert from pan. To serve, cut dessert into squares. Top with additional melon balls or wedges.