Prepare chocolate mousse according to package directions. Fold in chocolate syrup. Set the mousse aside in the refrigerator.
Combine 1 cup of the raspberries and the confectioners sugar in a food processor or blender. Whirl until pureed. Strain through fine sieve into bowl to remove seeds.
Prepare instant vanilla mousse according to package directions. Divide in half. Fold raspberry puree into one of the halves.
Equally divide chocolate mousse among ten 8-ounce glass dessert dishes, about a scant 1/3 cup mousse each. Arrange 1/2 cup of the remaining raspberries, dividing equally, among the dessert dishes.
Equally divide raspberry-vanilla mousse among the dishes. Spoon in remaining 1/2 cup of raspberries, dividing equally among dishes.
Equally divide remaining plain vanilla mousse among the dishes. Refrigerate 1 hour before serving. Garnish with additional berries if desired. Makes 10 servings.