Combine 5 tablespoons cold water and gelatin in a bowl. Let stand 5 minutes.

Combine sugar, 1/2 cup water, and wines in a saucepan over medium heat. Simmer until sugar has dissolved. Add gelatin mixture, and whisk until melted. Cook 1 minute. Remove from heat, and pour through a fine sieve into a 9-by-13-inch glass baking dish. Let cool completely.

Cut peel and pith from citrus. Cut each segment from membranes, then cut horizontally into 1/8- to 1/4-inch-thick slices (you will need 1 cup). Arrange in a single layer over gelatin mixture. Refrigerate, uncovered, overnight.

To unmold, run a knife around edge of dish. Using an offset spatula, gently coax gelatin from sides. Invert and turn out onto a cutting board. Trim edges, and cut into 1 1/4-inch squares. Serve immediately, or refrigerate, uncovered, up to 1 day.