Pour the water into a medium saucepan. Sprinkle the gelatin over the water. Let stand 1 minute. Bring the mixture to boiling, stirring constantly until gelatin dissolves. Remove from heat; turn off burner.
Stir in frozen juice concentrate. Stir until concentrate is melted. If you want deeper color, stir in food coloring.
Pour mixture into a foil-lined 8 x 8 x 2-inch baking pan. Cover, and chill until firm. Uncover, and turn the pan upside down onto a piece of foil sprayed with nonstick coating. Use cookie cutters or a table knife to cut the gelatin into shapes. Makes 36 (1-1/2-inch) gelatin pieces.