Place half of the red fruit into a mixing bowl and set the other half aside in a shallow 8x8” freezer-safe dish. Place half of the blue fruit into another mixing bowl and set the other half aside in another shallow 8x8” freezer-safe dish.
Divide the sugar, salt, lemon juice, and water between the mixing bowls and toss each separately to combine. Let the fruits marinate for about 30 minutes.
Once the fruits have marinated, purée them separately in a blender or food processor until smooth. Stir together the puréed red fruit and reserved red fruit in the freezer-safe dish. Stir together the puréed blue fruit and reserved blue fruit in the other freezer-safe dish. Transfer both dishes to the freezer.