1. Cut the watermelon into 2-inch-wide round slices. Trim away the rind. Cut the melon into 2-inch-square cubes.
2. Gently dab each side of the cubes on a paper towel to dry them slightly.
3. Pour the blue decoration sugar onto a plate.
4. Dip two sides of each cube into the sugar and place on a small plate, four cubes per serving.