Grease two pans that are roughly 6×5 inches with Pam or mildly flavored oil (like sunflower). Place two large heat-proof bowls on the counter. Place the raspberry puree in one and the blueberry puree in the other.
In a large pot, soften gelatin in cold water for five minutes. Stir in boiling water until gelatin dissolves. Add sugar and bring mixture to a boil over medium-high heat. Boil for 25 minutes, stirring constantly to prevent it from bubbling over.Pour half the hot gelatin mixture over the fruit puree in each of the prepared bowls. Working quickly, stir to combine. Pour each batch into one of the greased pans.
Refrigerate overnight (and up to a couple days).
Pour extra sugar onto a baking sheet. Using a knife to release the edges, gently remove the firm gelatin and place in the sugar, turning it to coat both sides. Transfer the gelatin to a cutting board and cut it into 3/4 inch cubes. (Note: Coating both sides with sugar was the most effective way I found to minimize the stickiness of the gelatin.) After they are cut, toss the pieces back into the sugar, tossing to coat. Transfer coated gumdrops to parchment paper.
Leave on the counter at room temperature for two days to crystalize.